Gravity - You're Full of Hot Air!
Gravity is a force that is always at work. If we want to move something, we must use a force to overcome gravity. You can understand how gravity works by doing these activities.
Get a balloon, blow it up and tie the end of the balloon. Let go of the balloon. What happens?
Gravity pulls on the balloon so it falls to the ground.
Now pick up the balloon. Tip your head back and blow the balloon up into the air. What did you observe this time?
The pushing force of your breath pushes the balloon into the air overcoming gravity. But when you stop blowing on the balloon, the balloon will fall down. Unless you keep blowing on the balloon, gravity takes over and causes the balloon to fall back to Earth.
Picture in your mind hopping on your bicycle or grabbing your skateboard. To get moving you must push with your legs. You are using a force to overcome gravity. Now find a hill to climb. As you move up the hill, notice how much more difficult it is to move forward. You have to push harder (with more force) to get up the hill because gravity is pulling you down. You have to overcome gravity to move forward up the hill.
A toy truck won't move up a hill or ramp by itself. Gravity keeps the truck from moving. A force must push or pull on the truck to make it move. Click the play arrow to watch the video below to see an example of this.