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a push or a pull

net force

the combination of all the forces acting on an object

balanced forces

two or more forces exerted on an object cancel each other out and do not change the object's velocity

unbalanced forces

two or more forces exerted on an object do not cancel each other out so the objects velocity changes

Newton's first law of motion

if the net force on an object is zero, the object at rest stays at rest, while the object in motion stays in motion


the force that brings nearly everything to a stop

Newton's second law of motion

the acceleration of an object equals the net force divided by the mass and is in the direction of the net force


the size of the gravitational force exerted on an object

center of mass

the point in an object that moves as if all the object's mass were concentrated at that point

Newton's third law of motion

forces always act in equal but opposite pairs

static friction

a force that prevents an object from moving

sliding friction

a force that opposes the motion that occurs when one solid surface slides over another

rolling friction

a force that opposes the motion that occurs when an object rolls over a surface


a force of attraction between objects that is due to their masses

air resistance

a force that opposes the motion of objects that move through the air


the rate at which velocity changes


the amount of matter in an object


the speed and direction of an object

centripetal force

a force that causes an object to move in a circular path

An object will________________ when the net force is zero.


_________will never speed up an object.


the friction that prevents an object from moving when a force is applied is __________ friction


The friction that slows down an object that slides is ___________ friction


A(n)_________helps reduce sliding friction.


Normal force is supplied by the ________ of the surface


The speed an object reaches when the force of gravity is balanced by the fore of air resistance is called ____________________.

terminal velocity

Earth has so much ____________ that it hardly accelerates when you push against it.


__________ friction keeps an object a rest.


A force can ____________

either push or pull

The unbalanced force that stops almost anything is _________________


An object will accelerate in the direction of the _______________

net force

A net force acting on an object changes the object's __________


Newton's__________ law of motion describes the connection between an object supplying force and the object receiving the force.


A force in the opposite direction to the motion of the object will cause the object to ____________

slow down

If an object is at rest, all forces acting on that object must be ____________


Why is it easy to miss an action reaction pair?

It is easy to miss an action reaction pair because one of the objects is often more massive and appears to be motionless

Why does friction never speed up an object?

If 2 objects are in contact, frictional forces always try to prevent one object from sliding on the other.

There is no __________ in time between the action and the reaction


One reason it's often easy to miss an action reaction pair is b/c of the _____________ of one of the objects


Action reaction forces are always the same _________ but are in opposite ___________


The ______________ is reached when the force of gravity; the size of the air resistance depends on the shape of an object and its speed

terminal velocity

An object can speed up, slow down or turn in the direction of the net force when the __________ forces act on it.


Galileo realized that an object could be in motion if the ________ acting on it were _____________. In real life, _____________ is the force that ________ _____objects down and causes them to ________. Newton's _________ law of motion described how forces cause the motion of objects to _________: An object at rest remains at rest and an object in motion continues to move in a ___________ line with constant _________if the net force action on it is _____.

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