Push and Pull

Background Information for Teachers

Young students know that pushing and pulling can affect the movement of an object. They have experienced it during their play and may intuitively understand what is happening in Figure 1. This lesson provides vocabulary to describe their observations, and develops the idea that science explains what happens around them.

Image Credit: Science Buddies
Figure 1. Two buffalo pulling equally hard in opposite directions does not allow either of them to move.

Scientists refer to a push or pull as a force. Forces can change the movement of objects (the object's speed and direction), but they do not always do so. Imagine a grocery cart standing still. You push on the handlebar to make it move (Figure 2, top left). If it is already moving, and you push it, you can make it move faster (Figure 2, top right). You can pull on the handle to make it slow down or stop, or you can push on the other side of the cart, opposite the direction of its motion, to make it stop (Figure 2, bottom left). You could even push it from the side to change the direction it moves. These actions all change the movement of the cart, but if you and another person were to push equally hard on opposite sides of the cart, your forces would cancel out and the cart's movement would not change (Figure 2, bottom right).

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies

Simple diagrams showing the forces and speed of a shopping cart when: a person pushes a shopping cart forward, pulls on a shopping cart to slow its forward motion, pushes on the front of the cart to slow it down, and pushes a cart against another person pushing in the opposite direction (cart does not move).

Figure 2. Pushing or pulling on a shopping cart can change its motion. Light blue arrows indicate the cart's speed before you take an action, dark blue arrows indicate its speed after you take the action, and red arrows indicate a push or pull.

How much a force affects the movement of an object depends on the size of the force. Imagine pushing on the shopping cart just a tiny bit— its motion would not change very much. Pushing harder will result in a bigger change in its motion. Similarly, if the cart is rolling towards you, a tiny push in the opposite direction will not be enough to stop it— you will have to push hard to stop the cart. In general, the more the movement needs to change (speed up, slow down, or change direction), the bigger the force causing the change needs to be. In this lesson plan, your students will explore these concepts when rolling a ball to each other.

An object's weight also determines how its motion is influenced by forces. An empty cart will roll away faster than a full cart when given a gentle push. This is studied in a second lesson, together with the concept that objects can push each other. One cart can roll into another one and cause it to roll away.

Additional Background Links

• Forces: Push and Pull, Ms Egan
• Force and Motion, Science Video for Kids
• Forces of Nature, Physics4Kids
• Motion: Push and Pull, Fast and Slow, Book written by Darlene Stille, illustrated by Sheree Boyd

Engage (20 minutes)

1. Play several rounds of tug-of-war. For the first round, one child competes with the teacher. In the second round, three students compete with the teacher and in the last round, half or the full class competes with the teacher. For each round:
   1. Let the students predict who will win. Ask a few students to explain why they made their prediction. Preferably, pick a first student and ask for a second student who made a different prediction. These explanations can shed light on misconceptions students have. Write misconceptions down so you can come back to these later in the lesson.
   2. Ask them to raise their hand if they think the teacher will win.
   3. Announce whether all, most, about half, a few, or no students believe the teacher will win. Write this overall prediction down, as you will come back to it later in the lesson.
   4. Compete. Write down who won next to the prediction.
   5. Ask whether the class' overall prediction was correct.
   6. For the last round, ask why their prediction for this round is different (ot is the same) compared the the other rounds. Why do they think (why don't they think) the number of students matters.
2. Optional: Read the book Equal Shmequal written by Virginia Kroll and illustrated by Philomena O'Neill.

   Ask the students what the goal is of the game the animals play in the book, and what the animals do to try to win. What makes a team win?

   The animals are playing a game where each team pulls on one end of a rope, trying to pull the other team over a line. The team that can pull the hardest wins. The animals pull as hard as they can. They form groups. More animals pulling together can pull harder than one animal all by itself. Animals that are bigger and weigh more can in general pull harder. The animals try to make the teams equal by making teams of equal weight.

3. Optional: This lesson assumes students understand the words "push" and "pull." You can assess students' knowledge of these and other directional words with a "Simon says" game. Use an object (e.g. a block, ball or book) and let students push/pull the object away/towards themselves, up/down, to the left/right, etc.

4. I competed with some students in a game of tug-of-war. What did I do to make the rope move?

   You pulled the rope to make it move.

   Tell the class they are going to explore how objects start and stop moving.

Explore (30 minutes)

Tell the students they will use balls for their experiment.

1. Divide the class into small groups of 2 to 3 students. Have them sit across from each other (or in a triangle) with enough space to roll a ball between them.
2. Explain the goal and the rules. During the experiment, students will roll the ball to each other. The ball must stay on the ground (no throwing), and for most of the experiment, they can only touch the ball with one finger at a time. If you are using bigger balls, you might decide to let the students use one hand.
3. Let the students roll the ball to each other, using only one finger, for a few minutes before starting the guided experiment.
4. For each of the four experiments listed below:
   1. State what they need to find out.
   2. Allow the students some time to explore.
   3. Ask students to discuss their findings with their partner.
   4. Bring their attention back to you and let the students report their findings.
   5. Demonstrate the reported ideas for the class or let a student do the demonstration. A bigger ball like a basket or soccer ball is preferred for the demonstration.
   6. Draw the findings for experiment 1-3 on the whiteboard. These drawings can also be found in the slideshow.

For more advanced students: provide an second ball that is considerably heavier or lighter and ask them to explore how mass changes their findings. You can also provide them with a straw and a drop of liquid paint on paper and tell the students they cannot touch the drop. Can they find how to make it move? Blowing towards to drop will create wind that push the drop forward. Can they make it go faster, change direction, etc.?

For struggling students: some extra time to experiment with the ball while you or another student sounds out what they are doing can help. This lesson can also easily be broken up in several parts. This can give you more occasions to provide examples throughout the day. If needed, let each group work at their own pace and guide them along when they are ready, and go over the drawings as a class after everyone is done exploring a few cases.

Experiment 1: What do you do to make the ball move?

After some experimentation, add the question: "How do you know which direction the ball will move?" You might need to explain that the direction indicates which way the ball is going.

If you see the students only push the ball, place the ball in the middle of the circle and ask one student to get the ball with one finger. Ask what they just did to get the ball moving.

What did you do to make the ball move?

You pushed or pulled the ball. If students mention "rolling" , point out that rolling is a type of push too, you place your hand on the ball and push it to make it roll. In the same way, when you hit the ball, you push it away. Hitting is a type of pushing. Tell the students how grabbing is a type of pulling towards you while demonstrate grabbing the ball.

Pushing or pulling the ball gets it to move. Pushing makes the ball move away from you; pulling makes the ball move towards you. Notice how the ball moves in the direction you push or pull. If you push it towards Lisa, it will move towards Lisa (replace Lisa with the name of a student). You may need to remind students that different actions, like hitting or rolling the ball, are all different types of pushes. Demonstrate the findings and make a drawing like the left side of Figure 3. Draw a person sitting next to a ball first. Write the word PUSH above the person. Next, draw the red arrow showing the pushing action, and demonstrate on a real ball what you just drew. Then, ask a student to draw an arrow showing which way the ball moves. Add the word "Start" next to the figure. Repeat this for the picture on the right illustrating a pull.

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 3. Illustration of how you push or pull to start a movement. The red arrow indicates the direction in which you push or pull, the blue arrow indicates the resulting movement of the ball.

Can you give me some examples of things that we move with pushes and pulls?

Some plausible answers are a toy car, a pencil, a book, a child on the swing, and a ball.

We now know how to make these objects move. What else would be nice to know?

Guide students into wanting to know how to stop or change the direction of moving objects. If needed, show how an object rolls off a table and ask what you need to know once you know how to make an object move?

Experiment 2: What do you do to stop a moving ball? You can use your whole hand for this exercise. Only one hand though. (If you are using bigger balls and they used one hand before, allow them to use both hands for this part.)

Pushing or pulling the ball can get the ball to stop. Note that not any push or pull will do the job. You need to push or pull against the movement of the ball and just hard enough. The students might state that they hold their hand out to stop the ball. You can clarify by stating, when the ball rolls into your hand, it pushed your hand, trying to move it away. You need to push back to stop this from happening. Similarly, you can pull a ball to prevent it from rolling away from you. Demonstrate the findings and make a drawing like Figure 4. Draw a person sitting next to a ball rolling towards him/her first. Then, ask a student what the person needs to do to stop the ball. Write the word PUSH above the person. Next, draw the red arrow showing the pushing action, and demonstrate on a real ball what you just drew. Add the word "Stop" next to the figure. Repeat this for a picture illustrating second motion (pull).

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 4. Illustration of how you push or pull to stop a movement. The red arrow indicates the direction in which you push or pull, the blue arrow indicates the initial movement of the ball.

Experiment 3: If students were working in pairs, join two pairs so they form groups of four students. Groups of three students work too.

Did anyone wonder what happens if you push a ball from the side while it is already moving? For example, you can push your ball with one finger to the person next to you, and without stopping it, they will try to touch it with one finger. Have a short discussion of what they think will happen.

Pushing or pulling a rolling ball in a direction different from the direction it is moving will make the ball change direction. After some time of free exploration, let one student show how a ball changes direction when it was rolling and is pushed from the side. Give specific directions to explore this part in more depth. For example, if Lisa, Camila, Peter, and Monte make a circle, you can say "Lisa starts the ball, she pushes it so it rolls to the person next to her which is Camila. You will need to find out how Camila can touch the ball, so it changes direction and rolls towards Peter. Then Peter will do something, so it changes direction and rolls towards Monte, etc." Demonstrate the finding and draw Figure 5 on the whiteboard. Draw a person sitting next to a ball rolling towards him/her first. Draw a figure sitting in the back. Then, ask a student what the person needs to do to make the ball roll towards the person sitting in the back. Write the word PUSH above the person. Next, draw the red arrow showing the pushing action, and demonstrate on a real ball what you just drew.

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 5. Illustration of how you push to change the direction a ball is moving in. The red arrow indicates the direction in which you push, the blue arrows indicate the movement of the ball before and after the push.

We already know how to start and stop the ball, and how to change the direction in which it moves. What else would you like to know? [Push a toy car so it rolls very slowly.]

Students might want to know how to make a ball roll fast or slow, or how to make a ball go faster or slower once it is rolling.

Experiment 4: What can we do to speed up or slow down a ball that is already rolling? In your small groups, change position so you sit in a line, all facing to the side. In a moment, the first person will get the ball rolling, and the last person in the line will stop the ball. What can the people in the middle do to speed up or slow down the rolling ball?

If your students are not familiar with the word, explain that speed is how fast something moves. "Speeding up" means that something moves faster, and "slowing down" means that something moves slower.

After some experimentation, ask the students to switch positions so every student has a chance to feel what it feels like to speed up or slow down a ball.

Pushing or pulling a rolling ball in the direction it is already moving will make the ball move faster. It will speed up. The harder you push or pull, the more the ball will speed up. Pushing or pulling a rolling ball against the direction it is already moving will make the ball move slower. It will slow down. The harder you push or pull, the more the ball will slow down, and eventually it will stop. It might even start rolling in the opposite direction! Again, if necessary, remind students that actions like "hit" or "roll" are different types of pushing, and actions like "grab" are a type of pulling.

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 6. Illustration of how adding a push or pull in the direction of the movement will speed up the ball. The red arrow indicates the direction in which you push or pull, the blue arrows indicates the movement of the ball.

What will happen if two people push at the same time? Demonstrate this for the whole class with a single student. This demonstration must be done with a bigger ball like a basketball, a soccer ball, or an even bigger ball. Let the student push in one direction while you push just hard enough in the other direction, so the ball does not move (Figure 7, left). Then find out what happens when you both push in the same direction at the same time (Figure 7, right). Discuss the results of both tests as a class.

If one person pushes in one direction and the other person pushes in the opposite direction equally hard, the ball will not move. If you have time, let your students try this too. Challenge them to push on opposite sides of a ball so it doesn't move. Allow them to use the bigger ball and both hands as that can make it much easier to keep the ball balanced. If both people push in the same direction, the ball will roll faster than when only one person pushes. Draw Figure 7 on the whiteboard.

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 7. Illustration of how two people pushing at the same time can influence the movement of a ball. The red arrows indicate the direction in which the push occurs, the blue arrow indicates the resulting movement of the ball.

Your students might ask what happens if two people push on the ball or object, but their pushes are not perfectly lined up with each other (for example, one person pushes forward, and one person pushes sideways). If so, try it and find out!

Reflect (10 minutes)

What did you learn?

Here are some things your students might say they learned. Use demonstrations to prompt students as needed. Hitting, rolling, or grabbing a ball is all a form of pushing or pulling a ball. We can push or pull on a ball to make it move. We can push or pull on a ball to make it stop. We can push or pull on a ball to change its direction, to make it turn. We can push or pull a ball to make it move faster or slower. We can push harder to make things speed up or slow down more quickly. We can push with several people on a ball to make it move faster, or not make it move at all. We can push in different directions.

Do you think this is only true for balls? Would other objects move in the same way? How can we know?

We can test with different objects like a block, a book, a pen, etc. Let the students test on something they have near them. Conclude that for those objects, pushes and pulls change how the objects move in similar ways.

Can you find examples of where you pushed or pulled to start or stop moving objects? Do you have examples of where you made objects speed up or down? What about times where you made them change direction?

Answers will depend on the experiences of the students.

Do you remember when we played the tug-of-war game? What happened when the teacher played against 1 student? Who won that game?

Look back to your notes to check who won the game and what the class predicted. Most likely, the teacher won this game. Try to remember the explanations the students gave for their prediction during the game. Did it reveal any misconceptions? This is a good time to correct those.

Why do you think that happened?

Pulling an object can make it move towards you, so each team pulls the rope to make it to move towards them. You can point to your drawing of Figure 3, "Pull to start" to support this statement. The teacher can pull harder, so the teacher wins this game.

What happened when the teacher played against the whole (or half) of the class? Who won that game?

Look back to your notes to check who won the game and what the class predicted. Maybe the rope did not move for a long time. If so, point that out too.

Which one of the drawings on the board can explain what happened here?

If the rope did not move for a long time, each side pulled just as hard. This is similar to the left picture of Figure 7, only now, both parties pull. If you read the book "Equal Shmequal," you can relate back to the drawing where both teams were equally strong, and the rope did not move. pulled in the same direction, they can create a bigger pull. Point to your drawing of the right part of Figure 7 to support the statement. More students in the team made it more likely for the team to win the game. In case one team stopped pulling and the rope suddenly moved fast, and maybe some people fell, point out how this is also expected. Suddenly, there is a way bigger pull in one direction and no pull in the other. Point to your drawing of Figure 3, "Pull to start" to support the statement. If you read the book "Equal Shmequal", you can relate back to the case where the bear stops pulling, and the rope suddenly moves a lot.

Optional: Give your students the worksheet to practice separating pushes from pulls.

Assess

Ask your students to identify examples of pushing and pulling on a playground or around the school, and ask them to describe the results of these pushes and pulls. Some examples are:

• Kicking a ball that is laying still. You push the ball away, which makes it move in the direction of the kick. If you kick hard, it will shoot off at high speed. If you kick softly, it will move slowly.
• Pushing someone on the swing. You push to make the child move or add a push in the direction of the movement to increase the child's speed.
• You can pull or push the classroom door to initiate movement.
• You can pull a book or backpack from the shelf.

Ask students to predict what will happen if you push an object like a book hard away from you, or soft to the left, etc.

Ask your students to demonstrate a push or pull and explain his or her action and the results of that action.

Ask your students examples of things they do at home that make things move, speed up, or change direction.

Ask students to predict who will win a tug of war game if one students pulls on one side and all other students on the other side. Ask them to explain their prediction.

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Physicist

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Career Profile

Physicists studying the world around them. How things move is part of it. They not only look at ordinary objects like balls, cars and books, but also at tiny objects, so small you cannot see them with your eyes, or huge ones like planets. Read more

Automotive Engineer

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Career Profile

Engineers are people who build and design things. There are many different types of engineers. Aerospace, automotive, and robotics engineers are a few examples. Engineers might design a wagon to make it easier for you to pull heavy things. Read more

Lesson Plan Variations

• An art project where you blow water-based paint around on paper can be used to reinforce and extend the learned concepts. Students blow through a straw to push the paint in the direction of choice. Ask the students how this is different and how it is similar to what they learned. During the lesson, people were always creating the push or pull. In this project, wind pushes the paint. Just like in the lesson, the paint moves in the direction of the push and harder pushes create more movement. Note that when you do not blow, the paint does not move. When there is no push or pull, the paint won't start moving.
• This lesson can be expanded with a lesson exploring how objects can push each other, and how weight influences motion.
• Show pictures of a sail boat or a toy sail boat. Let the students identify what typically pushes on these boats to make them move. Let the students create their own sail boat and explore how the direction in which you blow into the sail influences how the boat moves. You can replace the blowing with a fan. This activity can provide some ideas on how to build a boat. Construct a sail from a skewer (the mast) and sturdy paper or plastic to add to your boat.