Force
A push or a pull
Newton
The strength of a force is measured in the SI unit
net force
The combination of all forces acting on an object
unbalanced forces
can cause an object to start moving, stop moving, or change direction
balanced forces
Equal forces acting on an object in opposite directions
Friction
A force that opposes motion between two surfaces that are in contact
Static force
the friction that acts on objects that are not moving
sliding friction
two solid surfaces slide over each other
rolling friction
when an object rolls over a surface
fluid friction
friction that occurs as an object moves through a fluid
Gravity
A force that pulls objects toward each other
Weight
the force of gravity on a person or object at the surface of the planet
Freefall
when the only force acting on an object gravity
air resistance
Objects falling through air experience a type of fluid friction
projectile
an object that is thrown
Inertia
The tendency of an object to resist a change in motion
Momentum
a characteristic of a moving object that is related to the mass and the velocity of an object