What is pushing?
What is pulling?
A laboratory experiment from the
Little Shop of Physics at
Colorado State University
CMMAP
Reach for the sky.
Grade Level
• Activities designed to address
Kindergarten and 2nd Grade
Standards
Science Focus
• Newton’s 3rd Law
• Force
• Pushing & pulling
Time Required
• 20 minutes
When a popper leaps from a surface, what is
pushing on it to make it jump?
Extension 1:
• 15 minutes
Overview
Strange as it may seem, when you push or pull on an
object, the object is pushing or pulling on you. In this
activity, students will explore what is pushing or
pulling on objects to make them move.
Theory
When we push on something, we don’t often think of
the object pushing back, but it really does! When you
sit on a chair, you are pushing on the chair and the
chair is pushing back on you. The chair is pushing back
with an equal force, and pushing in the opposite
direction of your push. This idea is known as Newton’s
3rd Law.
Necessary materials:
• 6 popper toys
• 6 pullback cars
Extension 1:
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Tumble buggy
Propeller racer
String
Foam Core board
Straws
Thinking about an inanimate object like a chair, a table, or a rock pushing on someone or something, may
seem very strange. But if we think about what is happening at the molecular level, it may make more
sense.
When two objects touch, they both compress and then push back on each other. For example, if you are
out hiking, you may sit down on a rock to rest. The tiny particles (molecules) that make up both you and
the rock, compress when you sit down, and then push back, just like tiny springs. So when you push on
the rock by sitting on it, it pushes back with the same force in the opposite direction, pushing on you.
Doing the Experiment
Explain to your class that they will be exploring and working with two different toys, to help them learn
more about forces. Start with the poppers first. If you have students that haven’t played with poppers
before, show them how to turn them inside out and set them on a surface. Don’t let yours pop, however,
as this will be a fun discovery for the students that haven’t worked with them before.
Allow students to play with the poppers in their small groups for a few minutes, making sure everyone in
each group experiences what the poppers do and how to work them. Suggest that they try them on
different surfaces, such as: carpet, desks, the back of their hands, the palm of their hands, and more! Have
students discuss with their small group why the toy jumps into the air. Did the surface they placed the
popper on, make a difference in how the popper moved? Now hold a class discussion. What are the
poppers pushing on? Students may answer: the table, the floor, my hand, my thumb, the carpet,
someone’s head, etc.
Ask them to think about what is pushing on the popper. This is a difficult question. Tell your students that
if the popper changes its motion, something or someone is pushing on it.
Now let’s think about this some more. Have everyone in your class press on the palm of one of their
hands with a finger from the other hand. Have them observe what happens and discuss. The place where
you pressed your finger on your palm left a little dent, and then it pushed back out and the dent
disappeared. So you were pushing on your hand and your hand was pushing back. Let’s think about the
tiny particles that make up matter. When two objects touch, the molecules compress and then they push
back on each other. It is like they are little springs and when they are pushed, they spring back and push
on the other object. So, if the popper pushes on the table, the table pushes back on the popper. If the
popper pushes on someones’ head, the head pushes back on the popper, etc.
Collect the poppers and show them the next toy, a pullback race car. Let them play and explore with the
cars for a few minutes in their small groups and then pull them back together. Ask questions about how
the race car can move. Remind them that there has to be a force acting on the race car. What does the toy
do? ( You can nudge it forward by hitting it with your finger or you can push down on it and pull it
backwards. When you let go, it races forward.) When you nudge the car forward or pull back on the car,
are you applying a force? (Yes.) Are there any other forces changing the motion of the car? (Yes.) What
does the race car push on so it can move? (The table.) What is pushing back on the race car? (The table.)
Extension 1:
Before you begin the lesson:
Attach the tumble buggy to two long strings or pieces of yarn. One string is under the bottom rear of the
car, and one string is under the bottom front of the car. Tie the strings together above the car, so that you
can dangle the car in the air with one hand. Prepare the propeller car in the same way.
Place about ten straws on the table an inch or so apart and place a piece of foam core board on top of the
straws. If you choose not to do this, you can just lower the car onto a table in the lesson.
Begin the lesson:
Tell students that you are going to look at the tumble buggy and the propeller car again, to see what each
car is pushing on and what is pushing back on it. Turn on the tumble buggy and dangle it in the air. Ask
students if it is going anywhere. No. Why not? It isn’t pushing on anything. What would happen if we
lowered the car so it could push on the board? The car would move.
Lower the car and have students observe what happened. Discuss. Make sure to ask them what the car is
pushing on and what is pushing back on the car.
Now do the same thing with the propeller car. This will have an added feature, however. Since the
propeller car pulls air through its fan and the air pushes on the air behind it, it should move as you dangle
the car by the strings. Talk to your students about this and ask them what makes the propeller car move
forward. When the fan pushes air behind it, this air pushes on the air behind the car. The air behind the car
pushes back, and the racer moves forward.
Have students predict what will happen when you lower the propeller car onto the board. Watch what
happens as you do this, and discuss.
Summing Up:
After doing several of these activities, students will have a good sense, that when one object pushes on a
second object, the second object pushes back on the first object with an equal and opposite force. They
will also discover that without a force, their isn’t any motion.
For More Information
CMMAP, the Center for Multi-Scale Modeling of Atmospheric Processes: http://cmmap.colostate.edu
Little Shop of Physics: http://littleshop.physics.colostate.edu