Force and MotionPart 2: What are forces?

Pushes and Pulls

A force is a push or pull that acts on an object.

Push

When an object pulls or pushes another object, the first object is exerting a force on the second one.

Pull

Object 1 (the puppy) is pulling Object 2 (the girl’s hair).

Forces can make a moving object speed up, slow down, or change direction.

Magnitude

Forces have both magnitude and direction.

Magnitude means the strength of the force.

Magnitude

Remember that force can be measured.

Magnitude is measured in units called newtons(N).

Gravity

Every object in the universe exerts a gravitational pull on every other object.

Gravity

Everything that has mass has a gravitational pull. Right now, your desk's gravitational field is pulling on you, and your gravitational field is pulling on the desk. However, since gravity is a relatively weak force, unless you're an extremely large object like a planet, you can't feel this pull. We do, however, feel the pull of the Earth on us.

Gravity

Only an object that is really, really large like Earth is strong enough to be felt.

Gravity

Earth’s gravity pulls other objects toward its center.

Gravity

Every time you jump into the air, the Earth's gravitational field pulls you back down. If you use more force, you can jump higher, but you always return to the Earth.

Gravity

An apple falls to the ground because the force of gravity pulls it toward Earth’s center.

Gravity

Gravity causes the velocity of the apple to increase as it falls.

Gravity

After one second of falling, an apple’s velocity will be about 10 meters per second

10 m s

Gravity

After two seconds of falling, an apple’s velocity will be about

20 m downward. s

The Swing of a pendulum

A pendulum swings because of the force of gravity. When the pendulum is released, gravity pulls on it and make it swing downward. Gravity makes the pendulum increase its speed as it swings downward. When the pendulum starts to swing upward, the force of gravity slows the pendulum until it stops. Then the pendulum is pulled downward again and it swings in the other direction.

Gravity