Target grades: 3rd, 6th – 8th
Key Concepts: motion, force, balanced forces, unbalanced forces, net force, total force, sum of forces, cause and effect, interactions, push, pull, mass
Look at the pictures below of two people pulling on a cart of candy. Which way do you think the cart will move in each of the pictures below? Explain your predictions using drawings and words in the Forces and Motion Graphic Organizer
- Go to PhET Force and Motion Basics and click “Net Force” or use the simulation window below to test your predictions in a series of trials. Try new combinations!
Compare the predictions that you made above to what happens to the cart of candy in each trial. If some of your predictions are not right, use a different color pencil to correct them.
- Try more trials using different combinations of people from the red and blue teams. Draw or talk about what you discover. You can use the Forces and Motion Graphic Organizer table to keep track of your observations. Add more rows if you want.
Look at your tables. What are some “rules” that you can use to make predictions about which way the cart will move? You might ask yourself questions like:
a) Does it matter that the people are red or blue? Explain your answer.
b) Does a large person always win each competition? Provide evidence to support your answer.
c) If two people are pulling on opposite sides, does the cart always stay still? Explain your ideas.
d) Does it matter what part of the rope a person holds? Provide evidence to support your answer.
e) How does the “Sum of Forces” help you?
Try using the PhET Force and Motion Basics -- "Motion" screen to explore the impact of mass on the speed of a pushed object, such as a refrigerator, crate, or person:
1. What happens to the crate when you use the person to push it?
2. What is different if the person pushes more?
3. What do you notice if the person pushes against the crate, opposite to the direction that the crate is moving?
4. Compare pushing one crate to pushing two crates.
5. Try some of the other objects like the girl or the man. Describe a few things you discovered and new things you learned.
Ready for more? Explore applied, friction, and total forces in this extension from PhET Simulations here
Check out these miniature masters of force and motion in this SciFri video:
"Mini Speed Demons" produced by Flora Lichtman
Next Generation Science Standards:
- Performance Expectations: 3-PS2-1, 3-PS2-2, MS-PS2-2
- Disciplinary Core Ideas - PS2.A: Forces and Motion; PS2.B: Types of Interactions
- Crosscutting Ideas: Cause and effect, Patterns; Stability and Change
- Practices: Asking Questions and Defining Problems, Constructing Explanations and Designing Solutions, Engaging in Argument from Evidence, Analyzing and Interpreting Data, Planning and Carrying Out Investigations