Pushes, Pulls and Changes in Motion

You press a button to ring a doorbell. You tug your socks up. Both actions use a force. A force is a push or a pull.

Watch how you press or tug

A push presses away from you. Pushing a shopping cart, shutting a door, and kicking a ball are pushes. Your foot can push just as your hand can.

A pull tugs toward you. You pull a wagon by its handle. You pull a drawer out to reach a crayon. When you close the drawer, you push it back in. One job can use both kinds of force.

Imagine holding a door handle. You tug it toward your body, and the door opens. That is a pull. You press it away to close the door. That is a push. To name your action, look at the way you press or tug.

A force can act without movement

Put your hands against a wall and press. The wall stays still, but you are pushing. Movement is not needed for a push to happen.

In tug-of-war, you tug the rope toward your body. The other team might pull harder, making the rope slide away. Your action is still a pull. The rope's movement does not change the way you are tugging.

Find forces around you

People are not the only things that push and pull. A horse pulls a cart. A dog pulls on its leash. Wind pushes a sail and blows leaves along. Moving water pushes a toy boat down a stream.

Earth pulls things down toward the ground. This pull is called gravity. Let go of a ball, and Earth's pull makes it fall. Nobody needs to touch the falling ball to pull it down.

Your body can be the thing that moves, too. A friend pushes you on a swing. Someone pulls you on a sled. When you press your feet against a pool wall, the wall pushes back and you glide away. On a scooter, your foot pushes back against the ground, helping you move forward.

A tap and a big kick are both pushes. The tap is gentle. The kick is strong. You can describe a force by its strength and its direction.

Change how hard you push

Roll the same ball twice along the same floor. Start from the same line each time.

• With a gentle push, the ball rolls slowly. It stops about 2 big steps away.
• With a strong push, it rolls faster. It stops about 6 big steps away.

The stronger push makes the same ball move faster and farther. Keep the ball and floor the same to compare the pushes fairly. If you also change the ball, you will not know which change made the difference.

Before trying, make a prediction. This means saying what you think will happen and why. You could say, "A harder push will send the ball farther." Afterward, watch where it stops and check your idea.

Choose which way it goes

Direction means which way: left, right, up, down, forward, or backward. Push a still toy car to the right, and it starts rolling right. Pull a book up to lift it.

Keep the direction the same and change the strength. A gentle push left sends the car slowly left. A stronger push left sends it faster left. A stronger push does not mean a different direction.

Draw a force arrow

An arrow can show a force. Its point shows which way the push or pull goes. Its length shows how strong the force is.

Imagine a child pushing a box to the right. Start the arrow at the child's hands and point it right. Draw a short arrow for a gentle push. Draw a longer arrow for a stronger push.

For a child pulling a wagon, draw the arrow along the handle. Point it toward the child, the way the child tugs. To show a stronger pull, keep that direction and make the arrow longer.

Arrow length does not show how big the toy is. A tiny marble can have a long force arrow when someone flicks it hard. A large box can have a short arrow for a gentle push.

Watch a ball, a book, and a spinning top. They do not all move the same way. Words for movement help you tell someone exactly what you see.

Name the movement

Shape helps explain some movements. Balls and wheels are round, so they roll. A flat book slides along a tabletop. A bouncy ball springs up after landing. A dropped book usually lands and stays there.

One trip can have several movements. A ball rolls to a wall, hits it, and bounces back. Describe each part of the trip in order.

Tell how fast and which path

Fast and slow describe speed. A toy car racing down a steep ramp is fast. A snail moves slowly. You can also compare two things: "The car is faster than the snail."

A path is the route something takes. It can be straight, curved, zigzag, or round and round. A ball rolled across a flat, smooth floor follows a straight path until a push sends it a new way. A toy train follows the curves in its track.

Compare places

Position means where something is. Use a still object to help describe it. You might say, "The car is next to the door." Later, you say, "The car is under the table." Its place changed, so it moved.

A wall or a tree makes a useful still marker. A toy that was near the wall and is now far away has moved. Words such as behind, in front of, left, right, on, and under make the description clearer.

A spinning top can stay in one spot on the floor. It is still moving because its parts turn round and round. Looking only at where the whole top sits can make you miss its spinning movement.

A ball rests on flat grass. It stays there until something pushes or pulls it. A kick can start it rolling. Wind can start it moving, too.

Start in the direction you choose

To start a wagon, pull its handle forward. To start a toy car, push it from behind. The push or pull starts the still toy moving.

To stop a gently rolling ball, your hand can press back against it. Your hand gives the ball a push against its movement. A goalkeeper's hands push on a ball while catching it. A wall pushes on a toy car when the car hits it.

Practice stopping only slow toys, such as a gently rolled ball. Never step in front of a moving swing or bike to stop it.

The same ball moving faster needs a stronger push to stop quickly. You feel this when catching it. A hard throw presses harder on your hands than a gentle roll.

Follow a bowling ball

1. The bowling ball is still in your hand. You push it forward to start it.
2. It rolls down the lane and reaches the pins.
3. The ball pushes the pins. They begin to move and fall over.
4. A soft cushion at the end pushes back on the ball and stops it.

At the bump, both things push. The ball pushes a pin, and the pin pushes back on the ball. That push changes the ball's movement, too.

Try picturing two balls, one rolling and one still. When they bump, the rolling ball pushes the still one. The still ball begins to move. It also pushes back on the first ball, slowing that ball down.

Find what makes a toy stop

A rolling ball does not get tired. On grass, the grass pushes against its movement a little at a time. The ball slows down and stops. Air also pushes against moving things.

You may not see these small pushes as easily as a hand's push. Look for what the ball touches as it slows. A ball rolling into a patch of grass meets something that pushes against its movement.

A ball is already rolling. You can change its speed or send it a new way. Look at the way it is moving before choosing where to push.

Push along with the movement

To speed up a rolling ball, push it the same way it is going. A push from behind adds speed. A gentle push speeds it up a little. A stronger push speeds it up more.

A swing works this way, too. Push just as it moves away from you. Your push goes with its movement, so the swing goes faster and higher.

Push against the movement

To slow down the ball, push against the way it is going. Your hand in front presses back on it. A small push can slow it. A bigger push can bring it to a stop.

When you slow a scooter with your foot on the ground, the ground pushes back against your movement. Something is making that change happen.

Push from the side

A push from the side changes direction. A soccer player can kick a rolling ball sideways to send it toward a teammate. Pull a wagon handle left to turn the wagon left.

A gentle side push makes a small turn. A stronger side push makes a bigger turn. A ball that hits a wall gets a push back from the wall and bounces away.

Here is a ball's trip through a park. It rolls toward Maya. Her foot presses against it until it stops. She kicks it toward Leo, starting it again. It bumps the side of a bench, which pushes it onto a new path. Leo kicks it the way it is already rolling, making it speed up.

Look for Earth's pull

Earth pulls you down a slide and makes you speed up. Roll a ball gently uphill. It slows, stops for a moment, and rolls down again. Earth's pull changes its movement on the slope.

After a kick, your foot leaves the ball. Your foot's push has ended. The ball keeps rolling because it has not been stopped yet. The floor and air slow it little by little. A moving ball does not need your foot to keep touching it.

Press a lump of play dough with your palm. Its shape changes. A force can change how something looks as well as how it moves.

Try four changes

You squash a sponge in your hand. You stretch elastic by pulling its ends. You bend a pipe cleaner into a hook. You twist a wet cloth to squeeze water out.

The same piece of dough can change in several ways. Squash it into a pancake. Roll it into a snake, then pull to stretch it. Bend the long piece into a ring. Twist a long strip by turning one end each way.

Compare gentle and strong forces

A stronger push or pull makes a bigger change in shape. Think of elastic that starts 10 centimeters long.

1. A gentle pull stretches it to 14 centimeters.
2. From 10 to 14 is 4 centimeters longer.
3. A strong pull stretches it to 20 centimeters.
4. From 10 to 20 is 10 centimeters longer.

Both actions stretch the elastic. The stronger pull makes the larger change. Compare each new length with the starting length, not just with the other stretched length.

Notice changes in harder things

Soft things are easy to change, but harder things can change, too. A paper cup can be crushed. Aluminum foil can be crumpled. A cracker can snap. Breaking is a big change in shape.

A push can change shape and movement together. When you kick a soft ball, your foot squashes part of it. The ball also starts moving away. You might need to watch closely to see the quick squash.

Squeeze a sponge, then open your hand. The sponge returns to its old shape. Squash some play dough and let go. The dough stays flat. Letting go helps you tell these two kinds apart.

Test what happens afterward

1. Look closely at the starting shape.
2. Squash, stretch, bend, or twist the thing.
3. Let go.
4. Watch its shape after you let go.
5. Sort it into "springs back" or "stays changed."

A sponge, rubber band, and bouncy ball go in the "springs back" group. Play dough, foil, and a bent pipe cleaner go in the "stays changed" group. The change while you hold something is not enough to decide. Watch what happens next.

Feel the push or pull back

A springy, or elastic, thing returns to its old shape after you let go. As you squeeze a sponge, it pushes on your fingers. As you stretch a rubber band, it pulls on your fingers. This push or pull back helps it return.

Point a rubber band away from faces when stretching it. Let it go back slowly.

A springy thing can be damaged by too much force. A rubber band can snap if stretched too far. A toy spring pulled too far can stay long and wobbly. A bigger stretch is not a way to make it more springy.

Choose a shape that helps

A bouncy ball squashes against the ground when it lands. As it springs back, it pushes down on the ground. The ground pushes the ball up into the air. That upward push makes it bounce.

Sofa cushions, trampolines, and sneaker soles squash and spring back. They make landings softer. A hair tie stretches to fit around hair, then pulls back to hold it.

Other jobs need a shape that stays. Clay holds the shape of a bowl. Foil stays wrapped around a sandwich. A bent pipe cleaner keeps the hook you make.

Changing shape does not always mean breaking. A squeezed sponge can still soak up water. Flat play dough can be shaped again. Look at what the thing does after the change to decide whether it still works.

You can find out how a ramp changes a toy car's trip. A ramp is a slope with one end higher than the other. Rest a board or stiff cardboard on a low pile of books.

Plan what to change

Ask, "Does a higher ramp make the car roll farther?" Predict what you think will happen. You might say, "I think the higher ramp will send it farther."

A fair test changes one thing. For this test, change the number of books under the ramp. Keep these things the same:

• the car and the ramp board;
• the starting line on the board;
• the floor at the bottom;
• the way you let go and measure.

Hold the car at the starting line. Let go without pushing. Earth's pull makes it roll down. A little extra push on one try changes the test.

Measure each trip the same way

Wait until the car stops. Measure from the bottom end of the ramp to the back wheels. Use that same part of the car every time. Measuring to its front wheels on another try would change the distance you record.

A tape measure gives distances in centimeters. You can also count equal blocks or floor tiles along a straight line. Put blocks end to end without gaps. Keep the same measuring unit for all the trips you compare.

Repeat and choose the middle result

Do three tries at each height. The car may not stop in exactly the same place each time.

Suppose your distances are 48, 52, and 50 centimeters. Put them in order: 48, 50, 52. The middle result is 50 centimeters. Use that result for this height. Choosing 52 just because it is the farthest would leave out the other tries.

Keep a record

Write the height and result in a table. Each row keeps the two pieces together.

You can also draw a bar for each height. Start the bars at the same line. A taller bar shows a farther trip.

Compare your result with your prediction. It is fine if your idea was wrong. The test shows what happened.

Raise one end of a ramp, and the car starts higher. Earth's pull speeds the car up as it rolls down the slope. From higher up, it has farther to drop before reaching the floor.

Read the pattern

Here are results from one fair test. The car, board, starting line, and floor stayed the same. The car was released without a push.

The distances get bigger as the ramp gets higher. From the higher ramp, the car reaches the bottom faster and rolls farther across the floor.

Compare 2 books with 1 book. Count on from 50 to 95: the car went 45 centimeters farther. Compare 3 books with 1 book. From 50 to 130 is 80 centimeters farther.

The trips do not grow by the same amount each time. You can spot the pattern without promising an exact distance for the next try.

Predict the next trip

For the same setup with 4 books, predict a trip farther than 130 centimeters. Then test it. Your prediction gives a direction of change; measuring finds the distance.

You can also change where the car starts on the same ramp. Starting halfway down gives it less height to drop. It rolls a shorter distance across the floor than when released from the top.

Follow the whole trip

On the slope, Earth's pull makes the car speed up. On the flat floor, the floor and air slow it down until it stops. Nobody has to keep pushing it forward after it leaves the ramp.

The car went farther from the high ramp because it started higher. You let go each time, so a harder hand push did not cause the change.

Keep the ramp low enough for the car to roll smoothly onto the floor. A very steep ramp can make it bump or flip at the bottom. Then the trip changes in another way, making the distances hard to compare.

On a playground slide, starting at the top gives you more height to come down than starting halfway down the same slide. Earth's pull has more height to speed you up. The same idea helps explain the car's trip.

A toy car rolls across tile and then reaches a rug. It slows down more quickly on the rug. The top or outside of something is its surface.

Feel rough and smooth

A smooth surface feels flat and even, like tile or a wooden floor. A rough surface feels bumpy or scratchy, like a doormat or gravel. A soft towel can slow a car down, too.

On a smooth floor, the car rolls farther. On a rough or soft surface, it stops sooner. Those surfaces push against the moving car more, slowing it down faster.

Compare the floors fairly

Keep the car, ramp height, and starting line the same. Change only the surface at the bottom. Release the car without a push. Measure three trips on each surface and choose the middle result.

Here is a surface test using a 2-book ramp.

Tile gives the farthest trip. Carpet comes next. The towel gives the shortest trip. From 60 to 150 is 90 centimeters, so the tile trip is 90 centimeters farther than the carpet trip.

Look at sliding things, too

A wooden block slides farther across a smooth table than across sandpaper with the same gentle push. A sled slides easily on smooth, icy snow. Surface changes matter for sliding as well as rolling.

Hardness alone does not tell you how quickly something stops. A hard gravel path and a hard smooth floor can give very different trips. A soft towel can stop a toy car sooner than either smooth floor.

Find surfaces that help your feet

The bumpy bottoms of sneakers and rough stair strips help keep feet from sliding. A doormat gives your shoes a rough surface to grip.

Ice and wet floors are slippery. Shoes can slide easily on them. Walk slowly where it is slippery, and pay attention to a "Wet Floor" sign. People use sand to add grip on icy paths. Salt helps melt ice.

Your ball rolls straight ahead, but its target box is off to one side. You can build something that changes its path. A design is your plan for solving a problem.

Decide what should happen

Say the job clearly: "The ball needs to turn into the box." A wall set at a slant can push the ball from the side. A wall straight across its path may send it back toward the ramp instead.

Choose an idea, build it, and test it. Watch where the ball goes. Keep a count of how many tries reach the box.

Use results to improve a turn

1. Without a wall, the ball reaches the box 1 time in 5 tries.
2. Add a slanted cardboard wall. The ball reaches the box 4 times in 5 tries.
3. Move the wall a little closer to the box. It reaches the box 5 times in 5 tries.

The wall pushes the ball sideways when they touch. That push turns the ball toward the box. Comparing the counts shows that the wall helps. Moving the wall helped again.

Change one thing before testing again. If you move the wall and raise the ramp together, you will not know which change helped.

Choose a way to stop or speed up

For a stopping job, try a rough towel strip, a small uphill slope, or a soft bumper. Each gives a push against the rolling thing's movement.

Imagine a toy car that must stop before a table edge. A towel is placed near the edge. In three tries, the car stops on the towel every time. The towel slows it before it reaches the edge. You can build your own stopping course on the floor.

For a farther trip, start the car higher on its ramp or choose a smoother floor. A stronger push can also send a toy farther when your design uses a hand push.

Test the job you chose

A ball reaching a box once is a good start. Try several times before deciding the design works. Count a success only when the ball does the job you named. Stopping near a box is different from rolling inside it.

Bowling bumpers and mini-golf walls use side pushes to guide balls. Your cardboard wall does the same kind of job. The results help you choose where it should stand.