Science: Energy
Mr. Brovold
Motion and Forces Lecture Notes
MOTION = a change in position over a certain amount of time.
SPEED = the rate at which an object moves.
DISTANCE = the length between two places.
The speed of an object is determined by how much distance it covers during a
given amount of time.
Formula:
Speed = Distance/Time
300 km/5 hours
300/5
60 kilometres per hour
Also:
Distance = Speed x Time
CONSTANT SPEED = Does not change over time or distance
VELOCITY = Speed in a given direction
ACCELERATION = the rate of change in velocity (speeding up, slowing down,
changing direction.
FORCE = a push or pull on an object – gives energy to the object, sometimes
causing it to start moving, stop moving, or change direction.
In Hockey:
 The force of the stick causes the puck to move
 The moving puck is stopped by the goaltender
 The moving puck is deflected by another stick and changes direction
FRICTION:

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

a force opposing motion
is caused by two surfaces touching
Causes an object to slow down or stop
Surfaces of objects are not smooth – jagged edges of the objects catch on
each other
 Amount of friction depends on how hard the surfaces are forced together
and what the objects are made of.
 To move an object – exert a force greater than the force of friction
Sliding Friction = two objects sliding against each other
Rolling Friction = produced by objects such as wheels and ball bearings
Fluid Friction =
object moving through liquid
Air Resistance =
object moving through gases (air)
NEWTON’S LAWS OF MOTION
1. Law of Inertia
Objects that are at rest tend to stay at rest, and objects that are in motion tend to
stay at a constant velocity, unless acted upon by an external unbalanced force.
2. Law of Acceleration
Force is the product of mass and velocity. The law is often stated as:
F = ma
(Force equals mass times acceleration)
3. Law of Reciprocal Action
For every action, there is an equal and opposite reaction.
MASS is the measure of the amount of matter in an object
INERTIA
 property in matter that tends to resist any change in motion
 related to the mass of an object: more mass = more inertia
GRAVITY
 force that makes objects move towards the centre of the Earth;
 depends on the mass of two objects and the distance between them.
WEIGHT
 the measure of the force of gravity on an object’s mass. (W = m x g)
 Your weight will change as you move away from the centre of the Earth.
FORCE OF GRAVITY
 The acceleration of a falling object is due to the force of gravity between
the object and the Earth
 Objects fall to Earth at a rate of 9.8 metres per second, which increases by
this amount each second while it continues to fall.
 Air resistance (friction with the air) can slow the rate of acceleration of a
falling object.
 When the force of a falling object is equal to the force of air resistance,
there is no more acceleration = TERMINAL (final) VELOCITY.