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Notes: Motion and Forces
A. What is motion?
1. An object is in motion if it involves a change in
position relative to a reference point.
2. Distance is the total length of the route an
object travels when it moves.
a. Speed describes the change in position
(distance) during a period of time, without
respect to direction;
Formula: speed = distance / time
b. Velocity is the speed of an object and its
direction of motion; describes how position
changes over time (Ex. the speed of a car is
65 mph; the velocity of the car is 65 mph
traveling east)
3. Acceleration describes how velocity changes over
time, it can include an object’s speeding up, slowing
down, and/or changing direction
Formula: acceleration = (final speed – initial speed)
time
B. What is force?
1. A force is a push or pull on an object
2. balanced forces do not change an object’s motion
3. unbalanced forces cause the motion of an object to
change
4. types of forces – magnetic, electrical, gravity,
friction, buoyancy, tension
C. In the late 1600’s, Sir Isaac Newton identified three
basic laws of motion.
1. Newton’s First Law of Motion
a. An object at rest will remain at rest and an object
in motion will remain in motion unless acted
upon by an unbalanced force
b. Also called the law of inertia. Inertia – is the
tendency of an object to resist any change in
motion
1.) The amount of inertia an object has depends
on its mass. Mass is the amount of matter in
an object.
2.) The greater the mass of an object, the greater
its inertia
2. Newton’s Second Law of Motion
a. The overall force on an object is equal to the
mass of an object multiplied by the acceleration
of the object; Force = mass x acceleration
b. If the force on an object increases, then
acceleration will increase.
c. If the mass of an object increases, the acceleration
will decrease.
3. Newton’s Third Law of Motion
a. When one object exerts a force on another object,
the second object exerts an equal but opposite
force back on the first object.
b. This is known as the law of action-reaction
D. The Force of Gravity
1. Gravity is the force that pulls objects toward each
other.
2. Weight is the force of gravity on a person or object
at the surface of a planet
3. The law of universal gravitation states that the
force of gravity acts on all objects in the
universe.
4. The strength of gravity between two objects
depends on their masses and the distance
between them.
a. The greater the masses of the objects, the
stronger the pull of gravity.
b. The greater the distance between the
objects, the weaker the pull of gravity.