MS-PS2-4: Arguing from Evidence That Gravity Attracts and Depends on Mass
In plain English: MS-PS2-4 is the NGSS middle school performance expectation that asks students to construct and present arguments, using evidence, that gravity always pulls objects toward each other and that the pull depends on the masses of the objects. Evidence comes from spring scales, simulations and solar system charts. It is usually taught in middle school physical science.
Construct and present arguments using evidence to support the claim that gravitational interactions are attractive and depend on the masses of interacting objects.
Clarification Statement: Examples of evidence for arguments could include data generated from simulations or digital tools; and charts displaying mass, strength of interaction, distance from the Sun, and orbital periods of objects within the solar system.
Assessment Boundary: Assessment does not include Newton's Law of Gravitation or Kepler's Laws.
Next Generation Science Standards · Disciplinary Core Idea: Motion and Stability: Forces and Interactions · Official standard
Students build and present arguments, backed by evidence, for two claims about gravity: gravitational interactions are always attractive (they pull objects toward each other), and their strength depends on the masses of the interacting objects. They collect evidence with spring scales, read data from a gravity simulation and from a chart of the solar system, and turn that evidence into claim, evidence and reasoning arguments that they present to classmates.
The NGSS Clarification Statement says: "Examples of evidence for arguments could include data generated from simulations or digital tools; and charts displaying mass, strength of interaction, distance from the Sun, and orbital periods of objects within the solar system." The Assessment Boundary says: "Assessment does not include Newton's Law of Gravitation or Kepler's Laws." So students never calculate a gravitational force from a formula on this page. They read pulls from scales, simulations and charts and describe the patterns in words. Data sets marked invented are made up for teaching. Planet values are published values, rounded. The page uses one fact: near Earth's surface, Earth pulls on each kilogram of mass with about 9.8 newtons.
Learning Objectives
By the end of this lesson, students will be able to:
Use observations of falling and hanging objects as evidence that gravity pulls objects toward each other
Read data from spring scales, a gravity simulation and a solar system chart, and describe how the pull changes when a mass changes
Decide whether a comparison is fair by checking that only one thing (one mass) changes between the cases
Construct a claim, evidence and reasoning argument about gravity and present it to classmates
Prior Knowledge Required
Students should already be comfortable with:
The idea that Earth's gravity pulls objects down toward Earth 5-PS2-1
Forces as pushes or pulls that can be measured in newtons
Reading values from a table and a bar or line graph
The planets of the solar system and the idea of an orbit (a path around another object)
Hold a globe and ask a student to point to where they live. Tape a small paper figure there and another on the opposite side of the globe.
Warm-Up Prompt
"A student in our town and a student on the other side of Earth each drop a pencil at the same moment. Draw an arrow on the globe for each pencil. Do the two pencils fall in the same direction? What does that tell you about where gravity pulls?"
Collect a few drawings. Some students draw both arrows pointing "down the page." Ask: "If both arrows point the same way on the page, would the second pencil fall away from Earth?" Lead the class to see that both arrows point toward the center of Earth. Write the word attractive on the board: an attractive force pulls two objects toward each other.
Direct Instruction15 minutes
Key words.Gravity (a gravitational interaction) is a pull between any two objects that have mass. Mass is the amount of matter in an object, measured in kilograms (kg). Weight is the pull of a planet or moon on an object, a force measured in newtons (N). A small apple weighs about 1 N on Earth. An argument in science has three parts: a claim (the answer to the question), evidence (data or observations that support the claim) and reasoning (why the evidence supports the claim).
Today's two claims are: (1) gravitational interactions are attractive, and (2) the strength of the pull depends on the masses of the objects. Work through the examples and ask, each time, "Which part is the evidence? Which claim does it support?" Use Diagram 2 with the first example.
Evidence for attraction: which way is down?
Students in Canada, Kenya, Brazil and Australia each hang a metal washer on a string and drop a ball. On a globe, every string and every falling ball points toward the center of Earth, even though "down" in Australia is the opposite direction from "down" in Canada.
Result: Claim: Earth pulls objects toward itself. Evidence: in all four places the objects move toward Earth's center. Reasoning: a pull toward the other object is an attractive force.
Evidence from a simulation (invented data)
In a gravity simulation, sphere A has a mass of 1,000 kg and sphere B starts at 1,000 kg, 10 m away, in empty space. Only sphere B's mass is changed: 1,000, 2,000, 3,000, 4,000 and 5,000 kg. The simulation shows a pull of 0.67, 1.33, 2.00, 2.67 and 3.34 millionths of a newton (µN) on each sphere, and the arrows on both spheres always point toward the other sphere.
Result: Each time sphere B gets more mass, the pull gets stronger, and with 5 times the mass the pull is 5 times as strong. No setting makes the spheres push apart. The data support both claims.
Evidence from a solar system chart
Use the chart below. Saturn is about 9.6 times as far from the Sun as Earth is, yet the chart shows the Sun pulls on Saturn about as strongly as on Earth (1.04 compared with 1.0).
Result: Saturn has about 95 times the mass of Earth. Being farther away weakens the pull, but Saturn's much larger mass makes up for it. The pull depends on the mass of the planet.
Same bag, smaller world
An astronaut's 2.0 kg tool bag weighs 19.6 N on Earth. On the Moon, which has about 1/81 of Earth's mass, the same bag weighs about 3.2 N. Its mass is still 2.0 kg.
Result: The bag did not change, so the weaker pull comes from the other object in the interaction. The Moon has much less mass than Earth and pulls on the bag about 1/6 as hard.
Why don't books pull together?
A simulation shows that two 2.0 kg books 30 cm apart pull on each other with about 0.000000003 N. Earth pulls on each book with 19.6 N.
Result: The pull between the books is real but billions of times too small to notice, because both masses are small. Gravity is noticeable only when at least one object has a very large mass, like a planet.
Solar system chart (published values, rounded). Sun's pull computed by a digital tool from the published masses and distances, with the pull on Earth set to 1.
Planet
Mass (Earth = 1)
Distance from Sun (million km)
Orbital period (Earth years)
Sun's pull on planet (Earth = 1)
Mercury
0.055
58
0.24
0.37
Venus
0.82
108
0.62
1.6
Earth
1
150
1.00
1.0
Mars
0.11
228
1.88
0.046
Jupiter
318
779
11.9
11.7
Saturn
95
1,432
29.4
1.04
Uranus
14.5
2,867
84
0.040
Neptune
17.1
4,515
164
0.019
Point out how to read the chart: the orbital period is the time a planet takes to go once around the Sun. Every planet keeps going around the Sun, again and again, instead of flying off in a straight line: the Sun's pull keeps bending each path toward the Sun. That is more evidence that the pull is attractive. Distance matters too: a pull is weaker when the objects are farther apart. So a fair test of the mass claim compares objects at the same distance, or, as with Saturn, explains how mass outweighs distance.
Guided Practice15 minutes
Pairs analyze the invented simulation data below. A 500 kg space probe is placed 20,000 km from the center of five imaginary planets that differ only in mass. Pairs plot the pull against the planet's mass, then compare their graph with Diagram 1.
Guided practice data (invented, from a simulation): 500 kg probe, 20,000 km from each planet's center
Planet
Mass (Earth masses)
Pull on probe (N)
V
1
498
W
2
996
X
3
1,490
Y
5
2,490
Z
8
3,980
Plot the five points with planet mass on the horizontal axis and pull on the vertical axis. Label both axes with units.
Describe the pattern in one sentence. (As the planet's mass goes up, the pull on the probe goes up.)
Explain why this is a fair test of the mass claim: the probe, its mass and its distance stay the same, and only the planet's mass changes.
Write a claim, cite two data points as evidence, and add one sentence of reasoning.
Independent Practice10-15 minutes
Argument rounds. Each student writes a short argument on an index card for the claim "Gravity pulls objects toward each other, and the pull depends on their masses." The card must use one piece of evidence for attraction and one for mass, taken from today's examples, the chart or the guided practice. Students then present their card to three different partners, two minutes per round. After each round the listener checks three boxes: Did the speaker state the claim? Name specific evidence? Explain how the evidence supports the claim? Speakers revise their card after the last round.
Closure5 minutes
Exit ticket: "A classmate says, 'Gravity only acts on heavy things.' Write two sentences that answer this claim using evidence from today." Look for answers that say every object with mass takes part in gravity, and that the pull is tiny when both masses are small, like the two books. Return to the warm-up globe and ask students to redraw their arrows if needed.
Differentiation Strategies
For Struggling Students
Give a sentence frame: "I claim that ___. My evidence is ___. This supports my claim because ___."
Start with the spring scale and the globe before the simulation and the chart, so the evidence is something students can feel and see
Highlight one column of the solar system chart at a time, and ask one question per column
For Advanced Students
Ask students to find, in the chart, a pair of planets that cannot be used alone as evidence for the mass claim, and explain why
Have students plan a simulation test that would show whether the pull depends on the mass of both objects or only one, and say what they would keep the same
Ask students to compare the Moon and Earth: the Moon is also smaller than Earth, and standing closer to a center makes the pull stronger. Explain why the Moon's weaker pull still points to its smaller mass
Assessment Guidance
What to Look For
Check that students name specific evidence (a number from a table, a direction on the globe, a trend on a graph) instead of saying "the data show it." Look for students who confuse mass and weight, who think gravity needs air, or who think there is no gravity in space. When students compare two planets, check that they notice whether the distance also changed. Students should not use a gravity formula: the evidence is read from scales, simulations and charts.
02
Classroom Activities
3 Activities
1
Spring Scale and Plumb Line Evidence Lab
20 minGroups of 3-4
Groups measure how hard Earth pulls on objects of different mass with a spring scale, and use a plumb line (a weight hanging on a string) to observe the direction of the pull. They graph their data and write an argument.
Procedure
Zero the spring scale. Hang each object (slotted masses, or water bottles with their lids on whose mass you measured on a balance) one at a time and record the reading in newtons.
Make a table of mass (kg) and pull (N), then a graph with mass on the horizontal axis.
Tie a metal washer to a 50 cm string. Hold it still and mark the direction it hangs. Then look at the globe: if every group in the world did this, which way would their strings point?
Safety: hang only masses the scale is rated for, keep feet clear of hanging masses, and wipe up any water at once.
Sample Data (invented)
Mass 0.10, 0.20, 0.35, 0.50, 0.75 and 1.00 kg gave readings of 1.0, 2.0, 3.4, 4.9, 7.4 and 9.8 N.
Discussion Questions
In the sample data, every object with more mass gave a larger reading. Which claim does that support?
The scale reads Earth's pull on the object. Does the object pull on Earth too? What would you need to see that pull?
Why is a plumb line evidence that the pull is toward Earth, and not just "toward the floor"?
Modification for Distance Learning
Students use a kitchen or luggage scale at home with cans and bottles whose mass is printed on the label, change grams to kilograms, and post their table and graph.
2
Gravity Simulation Investigation
20 minPairs
Pairs use a free online gravity simulation that shows two objects, their masses and the pull on each. They change one mass at a time, keep the distance fixed, and record the pull. Then they try to find any setting that makes the objects push apart.
Procedure
Set object 1 to 100 kg and the distance to 2.0 m. Record the pull for object 2 at 100, 200, 300 and 400 kg.
Now keep object 2 at 100 kg and change object 1 the same way. Does it matter which object gets more mass?
Try the smallest and the largest masses and several distances. Record the direction of the arrows every time.
Sample Data (invented)
Object 1 at 100 kg, distance 2.0 m. Object 2 at 100, 200, 300 and 400 kg gave pulls of 0.17, 0.33, 0.50 and 0.67 µN (millionths of a newton). Swapping which object changed gave the same four pulls. In all 20 settings the pair tried, both arrows pointed toward the other object.
Discussion Questions
The pull grew in all four steps. What would the pull be for 0 kg, and what would that mean?
Swapping which object got the extra mass gave the same pulls. What does that tell you about the claim "the pull depends on the masses of both objects"?
A simulation is a model. What would make you trust its data, and what would you want to check with real objects?
Challenge Variation
Pairs predict, then test, what happens to the pull when they change both masses at the same time, and explain why that test makes the mass claim harder to read.
3
Solar System Argument Gallery
25 minGroups of 3
Each group uses the solar system chart from Direct Instruction to build a bar graph of the Sun's pull on the planets and an argument poster. Groups then present their posters, and classmates give feedback with a checklist.
Poster Requirements
A bar graph of the Sun's pull on four planets the group chooses, with a labeled scale.
A claim about the direction of the Sun's pull, with evidence from the orbital periods.
A claim about mass, with one pair of planets as evidence and a sentence that deals with their different distances.
A 90-second presentation in which every group member speaks.
Discussion Questions
Every planet in the chart keeps orbiting the Sun. What does that tell you about the direction of the Sun's pull?
Earth has more mass than Venus, but the Sun pulls harder on Venus. What else is different about the two planets that could explain this?
Which pair of planets did your group choose as mass evidence, and how did you handle the difference in distance?
Feedback Checklist
For each poster, listeners mark: the claim is clear; the evidence uses numbers from the chart; the reasoning explains why the evidence supports the claim; the group dealt with distance. Each listener writes one question for the group.
Modification for Distance Learning
Groups build their poster as one slide and record a 90-second video. Classmates post feedback with the same checklist.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Pull on the Same Probe from Planets of Different Mass (Invented Data)
The guided practice data, drawn to scale: a 500 kg probe 20,000 km from the center of five imaginary planets. Only the planet's mass changes. The points rise along a straight line through the origin, so a planet with more mass pulls harder on the probe.
Diagram 2: Down Means Toward Earth's Center
Dropped objects in four places on Earth all fall toward Earth's center, so "down" points in different directions on the page. The pull is toward the other object: gravity is attractive. The drawing is not to scale.
04
Homework Assignment
~30 min
MS-PS2-4 Homework: Building Arguments About Gravity
Directions: Data sets marked invented are made up for practice; planet values are published values, rounded. Near Earth's surface, Earth pulls on each kilogram with about 9.8 N. End every problem with a claim, the evidence you used and one sentence of reasoning. Do not use a gravity formula: use the data.
Part 1: Reading the Evidence (Problems 1-3)
At an airport, a luggage scale measures Earth's pull on four suitcases (invented data): 5 kg reads 49 N, 10 kg reads 98 N, 15 kg reads 147 N and 23 kg reads 225 N. (a) Make a line graph of pull against mass. (b) Describe the pattern. (c) Write a claim about Earth's pull and the mass of the object, with evidence.
Published values: Mars has about twice the mass of Mercury, but a 1 kg rock weighs about 3.7 N on the surface of either planet. A student says, "This proves that mass does not affect gravity." (a) Mars is also much wider than Mercury, so its surface is farther from its center. Why does that make this an unfair comparison? (b) Describe a fair comparison that would test the effect of the planet's mass.
A gravity simulation gives these invented results. Trial 1: 200 kg and 200 kg, 5 m apart, pull 0.11 µN. Trial 2: 200 kg and 400 kg, 5 m apart, pull 0.21 µN. Trial 3: 200 kg and 400 kg, 10 m apart, pull 0.05 µN. Trial 4: 200 kg and 800 kg, 5 m apart, pull 0.43 µN. In every trial both arrows pointed toward the other object. (a) Which trials can you compare to test the effect of mass? Explain. (b) What do those trials show? (c) What claim do the arrows support?
Part 2: Arguments from the Solar System (Problems 4-6)
Use the solar system chart in the lesson. (a) Make a bar graph of the Sun's pull on Mercury, Venus, Earth and Mars. (b) Venus is almost twice as far from the Sun as Mercury, yet the Sun pulls harder on Venus. About how many times harder? (c) Use the masses to explain why.
Write a one-minute talk for a class of fifth graders that answers "Why do things fall down, and why does the Moon stay near Earth?" Use at least two pieces of evidence from this unit, include one sketch you would show, and end with your claim.
The Perseverance rover has a mass of about 1,025 kg. On Earth it weighs about 10,000 N; on Mars it weighs about 3,800 N. Mars has about 1/9 of Earth's mass. (a) Did the rover's mass change on the trip? (b) Which object in the interaction changed? (c) Write an argument that the weaker pull on Mars is evidence for the mass claim.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Claim
States a clear claim that answers the question (attractive, depends on mass, or both)
Claim is present but vague or only partly answers the question
Evidence
Cites specific data (values, directions, graph trends) and checks that the comparison is fair
Cites data in general terms, or uses an unfair comparison without noticing
Reasoning
Explains how the evidence supports the claim, using the idea of an attractive pull that depends on mass
Restates the evidence without explaining the link to the claim
Graphs and Presentation
Graphs have labeled axes with units; the talk or argument is clear to the audience
Graph or talk is missing a label, a unit or a clear ending
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Data sets marked invented are made up for practice, and planet values are published values, rounded. Near Earth's surface, Earth pulls on each kilogram with about 9.8 N. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which observation is the best evidence that the gravitational interaction between Earth and other objects is attractive?
Answer: C
Objects in every country fall toward Earth's center, so the pull always points toward the other object: it is attractive. Choice B is about how strong the pull is, not its direction. Choice A is about orbits and distance, and choice D is about sound, not the direction of the pull.
Question 2 of 20 · Multiple Choice
A student hangs bags of rice on a spring scale (invented data): 0.5 kg reads 4.9 N, 1.0 kg reads 9.8 N and 1.5 kg reads 14.7 N. Which claim do these data best support?
Answer: B
Every bag with more mass gave a larger reading, so Earth pulls harder on objects with more mass. Choice A ignores the change in the readings. Choice C reverses the trend in the data. Choice D gets the direction wrong: the scale stretches downward.
Question 3 of 20 · Multiple Choice
The same spring scale as in the last question is used for a 2.5 kg bag of rice. If the pattern continues, what should it read?
Answer: C
Each kilogram adds 9.8 N, so 2.5 kg reads 2.5 × 9.8 = 24.5 N. Choice A assumes Earth pulls the same on every object. Choice B writes the mass as if it were the force. Choice D uses 9.8 N for each half kilogram instead of each kilogram (5 × 9.8 = 49.0).
Question 4 of 20 · Multiple Choice
In a gravity simulation (invented data), sphere A stays at 500 kg and the distance stays at 4 m. Sphere B is set to 500, 1,000, 1,500 and 2,000 kg, and the pull is 1.04, 2.09, 3.13 and 4.17 µN. What do these data show?
Answer: A
Only sphere B's mass changed, and every increase gave a stronger pull, so the pull depends on B's mass. Choice B cannot be right because the distance never changed. Choice C ignores the increase from 500 to 1,000 kg. Choice D is wrong because sphere A feels the same growing pull that sphere B does.
Question 5 of 20 · Multiple Choice
Which result, if it were real, would go against the claim that gravitational interactions are attractive?
Answer: B
Objects that start at rest and move apart would mean a push, not a pull, so choice B would go against the claim. Choice A is a weak attraction, which the claim allows. Choice C is about distance, and choice D supports the mass claim instead of going against attraction.
Question 6 of 20 · Multiple Choice
Use the solar system chart. Jupiter is about 3.4 times as far from the Sun as Mars, yet the Sun pulls on Jupiter about 250 times as hard. Which fact best explains this?
Answer: C
Jupiter's mass is 318 Earth masses and Mars's is 0.11, about 3,000 times as much. The extra mass more than makes up for the greater distance. Choice A is a result of the orbit, not its cause. Choices B and D describe what Jupiter is made of or how it looks, which the chart does not link to the pull.
Question 7 of 20 · Multiple Choice
On Mars, a 1 kg object weighs about 3.7 N. A rover collects a 6.0 kg sample box. About how much does the box weigh on Mars?
Answer: A
Each kilogram weighs about 3.7 N on Mars, so 6.0 kg weighs about 6.0 × 3.7 ≈ 22 N. Choice B is the box's weight on Earth (6.0 × 9.8 ≈ 59 N). Choice C writes the mass as a force. Choice D is the weight of only 1 kg.
Question 8 of 20 · Multiple Choice
Use the solar system chart. Neptune has more mass than Uranus (17.1 compared with 14.5 Earth masses), yet the Sun pulls on Uranus about twice as hard. What best explains this?
Answer: D
Uranus is about 2,870 million km from the Sun and Neptune about 4,520 million km. The greater distance weakens the pull on Neptune more than its extra mass strengthens it, so this pair alone cannot test the mass claim. Choice A goes too far: the two planets differ in two ways, so the pair cannot show that mass has no effect. Choice B is a result of the orbit, not a cause of the pull. Choice C contradicts the evidence that gravity always attracts.
Question 9 of 20 · Multiple Choice
Two loaded shopping carts are parked side by side in a store parking lot. Why don't they roll toward each other?
Answer: B
Any two objects with mass attract, but for carts the pull is far too small to overcome the friction holding them in place. Choices A and C wrongly limit gravity to certain objects or places. Choice D contradicts the evidence that gravity is always attractive.
Question 10 of 20 · Multiple Choice
A class wants evidence that the pull depends on mass. Which investigation gives the best evidence?
Answer: D
Only the mass changes from one object to the next, so any change in the reading comes from the mass. Choice A never changes the mass. Choice B shows the direction of the pull (attraction), not its dependence on mass. Choice C mixes in air resistance and wind.
Question 11 of 20 · Multiple Choice
Which statement about gravity is supported by the evidence in this lesson?
Answer: D
The simulations show a pull between any two masses, even small ones, and the pull always points toward the other object. Choice A confuses "too small to notice" with "none." Choice B is wrong because gravity acts across empty space: the Sun's pull holds the planets in orbit with no air in between. Choice C contradicts the falling-object evidence.
Question 12 of 20 · Multiple Choice
A line graph shows Earth's pull (N) against the mass (kg) of several objects. The line starts at zero and rises from left to right. What does the graph show?
Answer: A
A rising line means that as mass increases, the pull increases. Choice C would be a flat line. Choice B is about falling speed, which this graph does not show. Choice D reverses the trend.
Question 13 of 20 · Multiple Choice
A student's argument reads: (1) "Gravity depends on mass." (2) "A probe 20,000 km from a planet with twice the mass felt twice the pull." (3) "Since only the planet's mass changed, the stronger pull must come from the extra mass." Which sentence is the reasoning?
Answer: C
Sentence 3 explains why the evidence supports the claim, which is the job of reasoning. Sentence 1 is the claim, and sentence 2 is the evidence (a data comparison). Choice D misses that sentence 3 links the two.
Question 14 of 20 · Multiple Choice
A scientist wants to compare the pull of two planets on the same 300 kg probe. Which setup is a fair test of the effect of the planet's mass?
Answer: B
Keeping the same probe at the same distance from each center means only the planet's mass differs. Choice A changes the distance too, so a difference in pull could come from distance. Choice C changes the probe's mass. Choice D lets the distance vary without control.
Question 15 of 20 · Short Answer
A simulation places a 400 kg probe 30,000 km from the center of Planet P and, separately, at the same distance from Planet Q (invented data). Planet P has 6 Earth masses and pulls on the probe with 1,060 N. Planet Q has 2 Earth masses and pulls with 354 N. Write a claim, cite the evidence and give your reasoning.
Claim: the pull of a planet depends on its mass: more mass, stronger pull. Evidence: Planet P has 3 times the mass of Planet Q and pulls about 3 times as hard (1,060 N compared with 354 N). Reasoning: the probe and the distance were the same, so the only difference that could change the pull is the planet's mass.
Question 16 of 20 · Short Answer
Astronauts float inside the International Space Station, which orbits about 400 km above Earth. A student says, "This proves there is no gravity in space." Give two pieces of evidence against this claim.
Sample answer: (1) The station keeps circling Earth instead of flying off in a straight line, so something keeps pulling it toward Earth: Earth's gravity. (2) Measurements show that Earth's pull at that height is still about 90% as strong as at the surface. Astronauts float because they and the station fall around Earth together, not because the pull is gone. Claim: gravity acts in space, and it is attractive.
Question 17 of 20 · Short Answer
In 1971, Apollo 15 astronaut David Scott dropped a hammer and a falcon feather on the Moon, where there is no air. Both fell to the ground and landed at the same time. Which claim from this lesson does this observation support, and which mistaken idea does it rule out?
It supports the claim that gravitational interactions are attractive: the Moon pulled both objects toward itself. It rules out the idea that gravity needs air (or that air pushes objects down), because there is no air on the Moon and both objects still fell.
Question 18 of 20 · Short Answer
A student uses a gravity simulation. She changes object 1 from 100 kg to 200 kg and, at the same time, moves the objects from 2 m apart to 4 m apart. The pull goes down, so she concludes, "More mass makes a weaker pull." Evaluate her conclusion and describe a better test.
The conclusion is not supported: she changed two things at once (mass and distance), so the drop in pull could come from the greater distance. A better test changes only the mass of object 1 and keeps object 2's mass and the distance the same, then records the pull for several masses. If the pull rises as the mass rises, the data support the claim that more mass makes a stronger pull.
Question 19 of 20 · Short Answer
The Moon travels around Earth about once every 27 days instead of moving off into space in a straight line. Use the idea of an attractive force to explain why.
Earth's gravity pulls the Moon toward Earth at every point of its path. The Moon is moving sideways, so the pull does not drag it into Earth, but it keeps bending the Moon's path into a loop around Earth. Without an attractive pull, the Moon would keep going in a straight line.
Question 20 of 20 · Short Answer
Write a two-sentence argument a sixth grader could present to answer the question "Does gravity ever push objects apart?" Include a claim and one piece of evidence.
Sample answer: Claim: No, gravity always pulls objects toward each other. Evidence: in a gravity simulation, every setting we tried showed both arrows pointing toward the other object, and on Earth dropped objects in every country fall toward Earth's center. Accept any accurate evidence from the unit that shows a pull toward the other object.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-PS2-4 mean?
MS-PS2-4 asks middle school students to build and present evidence-based arguments that gravity is always a pull between objects and that its strength depends on their masses. The code stands for Middle School, Physical Science, core idea 2 (Motion and Stability: Forces and Interactions), performance expectation 4. The practice is argument: students must use evidence, not just state the facts.
Does MS-PS2-4 include Newton's law of gravitation?
No. The Assessment Boundary says assessment does not include Newton's Law of Gravitation or Kepler's Laws. Students describe patterns in data from scales, simulations and charts in words. Calculating gravitational forces with a formula is beyond this standard and comes in high school with HS-PS2-4.
What counts as evidence that gravity is attractive?
Any observation that shows objects moving or pulled toward each other. Examples: dropped objects in every country fall toward Earth's center; a plumb line points toward Earth; planets and moons keep orbiting the object they circle; a simulation shows both force arrows pointing toward the other object.
What is the difference between mass and weight?
Mass is the amount of matter in an object, in kilograms, and it is the same everywhere. Weight is the pull of a planet or moon on the object, in newtons, and it changes from place to place. A 2.0 kg bag has the same mass on Earth and on the Moon, but it weighs about 19.6 N on Earth and about 3.2 N on the Moon.
Why don't we feel the gravity between ordinary objects?
Because the pull is tiny when both masses are small. Two books on a desk attract each other, but with billions of times less force than Earth pulls on either book, so friction easily holds them still. Gravity becomes noticeable when at least one object has a very large mass, like a planet or a star.
How do you use a solar system chart as evidence for MS-PS2-4?
The Clarification Statement suggests charts of mass, strength of interaction, distance from the Sun and orbital period. Orbital periods show that every planet keeps circling the Sun, which is evidence of an attractive pull. To argue about mass, compare the Sun's pull on two planets and account for their distances: Saturn is much farther than Earth but feels about the same pull, because it has about 95 times the mass.
What simulations work for MS-PS2-4?
Any free gravity simulation that shows two objects, lets students change each mass and the distance, and displays the pull and its direction. Students should change one mass at a time with the distance fixed, and they should test whether any setting produces a push. Remind them that a simulation is a model and that its results should match real observations.
What mistakes do students make when arguing about gravity?
Common ones are saying there is no gravity in space, thinking gravity needs air, mixing up mass and weight, and comparing two planets at very different distances as if only mass differed. Another is an argument with a claim and data but no reasoning sentence that links them.
Is MS-PS2-4 taught in grade 6, 7 or 8?
It depends on the school. NGSS sets middle school standards for grades 6-8 as a band, and many schools teach forces and gravity in grade 8 physical science, while integrated courses may place it in grade 6 or 7. It pairs well with MS-ESS1-2, the role of gravity in the solar system.
What comes after MS-PS2-4?
In high school, HS-PS2-4 asks students to use Newton's law of gravitation to describe and predict the forces between objects, and HS-ESS1-4 uses math to predict orbits. The patterns from MS-PS2-4 (more mass, stronger pull; farther apart, weaker pull) become the starting point for those formulas.
07
Related Standards
5 standards
These standards connect to MS-PS2-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
5-PS2-1Prerequisite
Support an argument that Earth's gravitational force on objects is directed down
Lesson coming soon
Alongside
MS-ESS1-2Parallel
Model the role of gravity in the motions within galaxies and the solar system
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