Science - Chapter 2 (Forces and stuff)

Force

A push or pull on an object

contact force

A push or a pull on one object by another that is touching it

Mass

The amount of matter in an object

law of universal gravitation

States that all objects are attracted to each other by gravitational force

astronauts' weight and mass

Astronauts in orbit around Earth are not weightless. Their weight is about 90%

Friction

A force that resists the motion of two surfaces that are touching

static friction

Prevents surfaces from sliding past each other

sliding friction

Opposes the motion of surfaces sliding past each other

balanced force

Forces acting on an object that combine and form a net force of zero

unbalanced force

Forces acting on an object that combine and form a net force that is not zero

Newton's 1st law

If the net force on an object is zero the motion of the object does not change

Inertia

The tendency of an object to resist change in its motion

example of force changing motion

When you pedal a bike, the force of your foot on the pedal causes the wheels to turn faster and increase the speed of the bike

Newton's second law

The acceleration of an object is equal to the net force acting on the object divided by its mass

centripetal force

In circular motion, a force that acts perpendicular to the direction of motion, toward the center of the curve

satellite and gravity

Gravity pulls a satellite inward

Newton's third law

When one object exerts a force on a second object, the second object exerts a force of the same size but in the opposite direction on the first object

example of 3rd law

When a gymnast applies force against the floor, the floor applies force back

force pair

The forces two objects apply to each other

example of force pair

A Swimmer diving from a boat applies an action force against the boat. The boat applies a reaction force on the swimmer

Momentum

A measure of how hard it is to stop a moving object

law of conservation of momentum

The total momentum of a group of objects stays the same unless outside forces act on the object