Download Motion and Forces Study Guide

Motion & Forces Study Guide
(Sections: 1.1-1.3, 2.1-2.3, & 3.2 of the Motion and Forces Book)
Remember to review class worksheets and science notebook prior to the test and ask
the teacher in class if there are any questions.
Motion is change in position over a period of time.
Frame of referenceWhenever you describe something that is moving, you are comparing it with something
that is assumed to be stationary, or not moving. The background or object that is used
for comparison is called a frame of reference.
Relative motion - all motion is described relative to a particular frame of reference.
There is no correct frame of reference—they are all equally valid.
Speed:
The speed of an object refers to how fast an object moves.
To determine the speed at which an object travels, you need to know both the distance
an object moves and the amount of time needed to travel that distance.
To calculate an objects speed, you use the following formula
Speed = Distance / time
A car travels 150 km in two hours. What was its average speed?
Average speed = Total distance / Total time
The car travels 150 ÷ 2 = 75 km/hr
Speed = 75 km/hr
Remember the word DOT to remember the formula.
Units for speed = m/s, km/hr
Graphing motion -- position and time graph –
Speed can be calculated by calculating slope on a graph of position versus time.
Speed = Slope = Rise / Run = y2 – y1
x2 – x1
Therefore according
to the graph, the
speed of this object
is 3 m/s.
http://www.mathwarehouse.com/algebra/linear_equation/images/slope_given_2points/slope-of-a-line-picture.jpg
Position time graph
More steep the line,
the faster the person is
moving
P
O
S
I
T
I
O
N
(m)
http://www.golfranger.co.uk/images/distance_time.gif
Velocity:
 Velocity is the speed of an object in a particular direction.
 Velocity is different from speed because it indicates a direction.
 Velocity changes when the speed or the direction of an object changes.
For example, if a car goes around a curve in the road, its direction changes. Even if
speed remains constant, the velocity changes because the direction changes.
Example: Sara’s velocity was 75 km/hr northwest
Velocity time graph
Increasing speed
Decreasing speed
http://www.bbc.co.uk/schools/gcsebitesize/science/images/ph_forces02.gif
Force:
 A force is a push or a pull. A force transfers energy to an object, sometimes
causing it to start moving, stop moving, or change direction.
 When two forces are acting in the same direction, they add together. When two
forces are acting in the opposite direction, the total force is calculated by
subtracting them. When total force on an object is in one direction, the force is
called unbalanced. An unbalanced force changes the motion of an object.
 Forces that are in opposite directions and equal in size are called balanced forces.
When forces are balanced, there is no change in motion. Balanced forces have the
same effect as no force at all.
1.
If both forces are in the same direction, add the two together to get Net Force
2. If forces are in opposite directions, find the difference between the two numbers.
The object will be moved in the direction of the larger force.
http://teacher2.smithtown.k12.ny.us/ksiolos/Science/Science8/Science8Units/ForcesandMotion.htm
Friction
 Friction is a force that acts in a direction opposite to the motion of the moving
object. Friction will cause a moving object to slow down and finally stop.
 Amount of friction between two surfaces depends on how hard the surfaces are
forced together and on the materials of which the surfaces are made.
 The force you exert to move an object is in one direction. The force of friction is
in the opposite direction. Because the two forces combine by subtraction, you must
exert a force that is larger than the force of friction in order to move the object.
First law of motion (law of inertia)
An object at rest will remain at rest and an object in motion will remain in motion
at constant velocity unless acted upon by an unbalanced force.
 Inertia is the property of matter that tends to resist any change in motion.
 The more massive an object is, the more difficult it is to change its motion. The
more massive an object is, the more inertia it has. Thus the inertia of an object is
related to its mass.
Be able to explain the importance of seatbelts in car using inertia.

240 × 180 - physics4kids.com
Second law of motion
 Newton’s second law of motion explains how acceleration and force are related.
 The greater the force, the more the acceleration (mass stays the same).
 Acceleration = force / mass or Force=mass times acceleration
Simulation for second law of motionhttp://tinyurl.com/k4xtw2v
Third law of motion
 Every time one object exerts a force on another object, the second object exerts
a force that is equal in size and opposite direction back on the first object.
 The force that is exerted on an object and the force that the object exerts back
are known together as an action/reaction force pair. One force in the pair is called
the action force, and the other is called the reaction force.
 Action and reaction forces are not balanced forces as they act on different
objects. (Balanced forces act on a single object)