Forces Around Us

Forces Around UsBy Cindy Grigg1 Look around you, and chances are you'll see things moving. Cars move. People move. Elevators move up and down in tall buildings. Shopping carts move around in supermarkets. Balls fly through the air when they are thrown. You might not think about why these things move. Cars, elevators, and balls don't just move by themselves. Something is making them move. Forces make things move.2 A force is a push or a pull. If you had a heavy box to move across your room, you might push it or pull it. The force would be working on the box in the same direction. It wouldn't matter to the box if you pushed it or pulled it. The amount of force needed to move the box would be the same. The direction of the force would also be the same.3 When you push or pull a box, it is easy to see where the force is coming from. But it's harder to see forces at work when we think about a person or an animal moving. When you walk across the room, what force is making you move?4 When you take a step, your foot is pushing down on the floor. That push is the force that makes your body move. When your foot pushes down on the floor, the floor pushes back. If the floor didn't push back, your foot wouldn't stop pushing down. You wouldn't go anywhere. You might end up standing in a hole.5 Have you ever tried to walk in deep snow? It's much harder to walk in snow than it is on solid ground. The snow is too soft; it can't push back as hard as the ground does.6 Forces always occur in pairs. A push in one direction means something is pulling in the other direction. When you push a box across the floor in your room, what other forces are pulling on it?7 One is friction. Rub your hands together very fast. Do you feel heat? That heat is coming from the friction between your two hands. Whenever two things are rubbing against each other, friction is the force that slows them down. Tiny bits of matter on both surfaces rub against each other. As one surface rubs in one direction, the other surface rubs in the other direction. The two opposite forces create friction. Friction slows down the motion of both surfaces. Friction also makes heat. Some of the energy of motion changes into the energy of heat.8 Gravity is another force that pulls on the box when you push it across your room. You may already know that gravity is the force that pulls a ball to the ground when you throw it. Gravity is the force that pulls all things down toward the earth. If you jump up, gravity pulls you down. If you throw a ball, gravity pulls it to the ground. When you stand on a scale, the force of gravity is pushing down on you.9 As you push on the box, gravity is pulling on the box toward the ground. The two forces are not pushing and pulling in exactly opposite directions. Gravity is pulling straight down, and you are pushing sideways. The two forces are working against each other even though they are not directly opposite.10 Why do cars have wheels? Have you ever thought about that? A wheel rolls much easier than a box would. There is less friction between a rolling wheel and the ground than there would be between a flat surface like a box and the ground. That's why wheels were invented-they make things easier to move.11 Forces can be applied in different directions. Forces can be large or small. The direction a force is applied is the direction in which the object will move. Gravity is probably the most important force on earth. Forces are all around us! 1. What makes things move? Your answer 2. A force is a _. push pull Both a and b none of the above 3. Forces always occur in _. Your answer 4. Complete this sentence: Whenever two things are rubbing against each other, friction _. Your answer 5. Where there is friction, there is _. heat noise fire smoke 6. What is the name of the force that pulls all things down toward the earth? friction gravity magnetic force atomic force 7. Which of these would have less friction? a toy car with wheels rolling across the floor a rock being pushed across the sidewalk 8. An object will move _. opposite the direction the force is applied in the direction the force is applied both a and b