Science Experiments / Week 4
Week 4 of 6
Forces, Motion, and Friction
Big question
What makes things speed up, slow down, or stop?
- Ramp Racer Surface Test
- 45-60 minutes
This week follows the science loop
AskPredictTestObserveExplainImprove
The big idea
- A force is a push or a pull.
- Gravity is a force that pulls objects down, including down a ramp.
- Friction is a force that slows motion when two surfaces rub together.
- The texture of a surface changes how far or fast something moves across it.
Nothing moves or stops on its own - it takes a force, which is just a push or a pull. Gravity is a pull that tugs everything toward the ground. When you put a toy car at the top of a ramp, gravity pulls it down, and it speeds up. But when the car reaches the floor, it does not roll forever. Another force, friction, works against the motion. Friction happens when two surfaces rub against each other, and it slows things down. This week you will race a car down a ramp onto different surfaces and see how much the surface changes how far it travels.
Words to know
- Force
- A push or a pull that can start, stop, or change motion.
- Gravity
- The force that pulls objects down toward the ground.
- Friction
- A force that slows motion when two surfaces rub together.
- Motion
- When something is moving from one place to another.
- Surface
- The outside layer of something, like the top of a floor or a towel.
Materials
- A toy car or anything that rolls
- A board or piece of stiff cardboard for a ramp
- A few books to prop the ramp up
- A tape measure or ruler
- Surfaces to test: bare floor, a towel, sandpaper, and foil
- Tape to hold surfaces flat
Safety
- Keep the ramp steady so it does not slide or tip.
- Clear the path so the car does not roll into anyone.
- Do not roll heavy objects toward feet or off high tables.
Experiment: Ramp Racer Surface Test
Predict first
Before you touch any materials, write down what you think will happen in this experiment - and why. Making a prediction first is what turns building into science. You will compare your prediction to what you actually observe.
Steps
- 1
Ask: On which surface will the car roll the farthest after leaving the ramp?
- 2
Build a ramp by propping a board on some books. Mark a starting line at the top.
- 3
Predict: Order the surfaces from 'car rolls farthest' to 'car stops soonest.' Write it down.
- 4
Test fairly: Let the car go from the same starting line every time without pushing it, and keep the ramp the same height. Change only the surface at the bottom.
- 5
Observe: Measure how far the car travels past the end of the ramp on each surface.
- 6
Record each distance next to your prediction.
- 7
Improve: Try to make the car go even farther - lift the ramp higher, or pick the smoothest surface - and test what actually helps most.
Why it happens
Gravity pulls the car down the ramp, giving it motion and speed. When the car reaches the floor, friction between its wheels and the surface pushes back against that motion and slows it down. Rough or soft surfaces like sandpaper and a towel grip the wheels more, so there is more friction and the car stops sooner. Smooth surfaces have less friction, so the car keeps rolling farther. A higher ramp gives gravity more of a head start, so the car starts faster.
How engineers use this
Engineers use friction on purpose when they want things to stop or grip - like the rubber on shoe soles, car brakes, and tires. They also work to reduce friction when they want things to move easily - like wheels, slides, and the smooth blades of ice skates. Knowing when you want more or less friction is a real engineering choice.
What did you notice?
Look back at your prediction and your results, then talk these through together.
- Which surface let the car roll farthest? Which stopped it fastest?
- Why is it important to let the car go instead of pushing it?
- What force pulled the car down the ramp? What force slowed it at the bottom?
- Where do you feel friction in real life?
Reflect
Write which surface let the car travel farthest and explain why using the word friction.
Mini challenge
Set a target line on the floor and adjust your ramp so the car stops as close to it as you can.
Want to go further?
Raise the ramp higher and measure how the extra height changes the distance. Keep the same car and surface.
Before you finish
- I built a ramp and kept it the same height for each test.
- I predicted how each surface would change the distance.
- I measured how far the car rolled on each surface.
- I can explain the roles of gravity and friction.
- I changed something and tested to make the car go farther or hit a target.
Finished the experiment and your reflection? Mark this week complete to track your progress through the 6-week course.
Lab journal
Write your own science notes as you go - they follow the same loop you used this week. Notes are saved on this device only; nothing is sent anywhere. You can also print this lesson and write by hand.
What did you want to find out?
What did you think would happen, and why?
What one thing did you change to keep it a fair test?
What did you see, hear, or measure?
Use what you noticed as your evidence.
What would you change to make it work better?
Draw what happened
Sketch your experiment or your improved design, and circle the part you changed.