9 The Science of Fun

Unit 9 VOCABULARY 1 1 Listen and read. We use force to move. Force happens when we push or pull. Do you push or pull when you move on a swing? You do both. Look at this skier. To move, a skier pushes on the snow. A push can move a skier forward. It can also move a skier backward. Skaters pull, too. Look at these skaters. The more one skater pulls, the more they spin. The skaters don’t fall over because they know how to balance. How do skaters stop? They use force. Skaters push down hard on their skates. The skates connect with the ice. The ice and skates rub together. When two things rub together, it’s called friction. 2 Listen and repeat. a force A force can push or pull. happen What happens when skaters stop? push To close the door, push it. pull To open the door, pull it. a swing My brother is playing on the swings. a skater Look at those skaters. They’re wonderful! forward The car moves forward. backward On the swings, I move backward and forward. spin Can you stand on one leg and spin in a circle? fall over I often fall over and get bruises. balance I can’t balance very well when I skate. down To move, push down on the ice. connect Skates connect with the ice. rub It’s cold. Rub your hands together. friction Friction happens when two things rub together.

SONG 1 Listen, read, and sing. I’m on the Move! Push it, pull it, push it, pull it, push, pull. Push, pull, push, pull! Watch it go! If you spin around, and around and around and around, what you feel is force. If you fall down, down, down, down, down to the ground, that’s gravity, of course. I’m on the move. I’m in the groove. It’s amazing what you can do when you let force do the work for you! The more you push, the faster some things go. When you spin around, the force comes and goes. I’m on the move. I’m in the groove. It’s amazing what you can do when you let force do the work for you! The more you push, the faster some things go. When you spin around, the force comes and goes. Push it, pull it, push it, pull it, push, pull. Push, pull, push, pull! Watch it go! If you spin around, and around and around and around, what you feel is force. If you fall down, down, down, down, down to the ground, that’s gravity, of course. I’m on the move. I’m in the groove. It’s amazing what you can do when you let force do the work for you! I’m on the move!

GRAMMAR 1 Cause and effect with double comparatives The more one skater pulls, the more the other one spins. The more you push the swing, the faster it goes. The more you practice, the faster you run.

VOCABULARY 2 1 Listen and repeat. away from The boy is riding away from the others. direction The boy and the girl are riding in the same direction. toward The girl is running toward the fi nish line. lean Don’t lean on the table. It might break! gravity Gravity pulls you toward the center of the Earth. 2 Listen and stick. Work with a partner. Compare your answers. Pedro loves riding his bicycle. But his friends want to go to the swings. He decides to leave his friends and ride his bike. He gets on his bicycle and rides the playground. He knows there is a bike trail near the lake. When he gets there, he needs to decide: Right or left? What does he want to go? He goes right. The trail is not straight. It goes up and down, left and right. When he gets to the top, he starts going fast down the hill. He has to left to turn to the left and that’s when he sees a big tree is in the middle of the trail and he is riding the tree. Oh, no! He has to think quickly. He doesn’t want to brake and just fl y over the bicycle. Then he sees lots of dry leaves on the side of the trail. What does Pedro do? He brakes just a little and he lets pull him to the bed of leaves. It’s good he always wears a helmet! GRAMMAR 2 Definitions with which Gravity is a force which pulls you toward Earth. Skates are special shoes which you wear when you go ice skating.

READING 1 Listen and read. Up, Down,and All Around! You are going on a roller-coaster ride. Sit in the car and pull down the safety bar. Are you ready? Let’s go! First you go up a steep hill. The roller coaster goes slow. Next gravity pulls you down the hill. The roller coaster moves fast. You feel very light! A big circle, known as the “loop the loop,” is many people’s favorite. When you go fast up the circle, you feel heavy. Gravity is pulling you down. When you reach the top, you are high in the sky. And you’re hanging upside down! So why don’t you fall out of your seat? Your body wants to fly off, but the speed of the car and a force called centripetal force keep you moving in a circle, and keep you in your seat! The roller coaster uses friction to stop. If it stops quickly, your body wants to continue moving. That is called inertia. But the safety bars keep you in place! Not everyone loves roller coasters. They make some people feel dizzy or sick because the forces change. In fact we experience forces like friction, centripetal force, and gravity every day. For example you feel gravity when you jump with your bike and come down. You feel centripetal force when you turn, and you feel friction when you use the brakes to stop the bike. How do you want to experience the forces? Do you want to ride your bicycle or a roller coaster?