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Power point summary
unit 5
In textbook
Chapters 10 and11
Distance vs. Displacement
• Distance
Definition: The length of a path between two
points
remember to use SI Units (meters)
• Displacement
Definition: The position change
and direction of an object
The straight line between your
starting point and the finish point
Distance = 180 + 140 + 100 = 420
Displacement = 140 Right
Speed vs. Velocity
• Only one difference
• Speed is the distance an object moves in a given amount of time
s = d/t (unit = m / s)
The car speedometer shows you traveling at 35 m / s
• Velocity is speed with a direction
v = d/t (unit = m / s)
A man walked 5 miles east from his house every morning to get the mail
Changing Velocity
• Velocity can change in one of two ways:
1. A change in speed
2. A change in direction
Instantaneous vs. Average
• Instantaneous Speed or Velocity is the
distance divided by the time at a given
moment
• Average Speed or Velocity is the total distance
divided by the total time
Speed (distance vs. time)
Always label time in the x axis
35
Distance (meters)
30
25
20
15
10
5
1
2
3
Time (sec)
4
5
6
7
Increasing velocity
35
Distance (meters)
30
25
20
15
10
5
1
2
3
4
5
Time (s)
6
7
Constant velocity
35
30
Velocity (m/s)
25
20
15
10
5
1
2
3
Time (sec)
4
5
6
7
Acceleration
• Acceleration – change in velocity per unit of time
• a = Δv or vf – vi
t
t
• Remember: Like velocity, Acceleration includes direction
• Acceleration can change by speed or by direction
What is a Force
• A Push or pull that acts on an object
• Units is a Newton (N)
• Examples of force
– The wind
– Any sport
– Car crashes
Newton’s First Law of Motion
• An object will remain at rest or constant
velocity unless a force acts upon it.
– A force is a push or a pull.
• INERTIA: an object’s resistance to a change in
motion. Inertia is dependent on an objects
mass.
Newton’s Second Law of Motion
• When a net force acts on an object, the
object to accelerate in the direction of the
net force
• F = ma
2nd law
• What does F=ma really mean
• Mass and acceleration are proportional to the
force
– If mass or acceleration increases – the force will
also increase
– If the force decreases - mass or acceleration
decreases
– This is called a directionally proportional
What is a Newton
Unit of force
abv = N
N = kg x m/s2
Gravity – Law of Gravitation
• The attractive force of two objects upon
each other
• Affected by:
1. Distance between the objects
2. Mass of the objects
Why???
• Would you weigh more on Earth or on the
moon?
• Why do you think you weigh more on Earth
than on the moon?
• The moon is 1/6 the size of earth so the
moon’s gravity is…
• 1/6 the gravity of the earth
Mass Vs Weight
• Mass – constant, is defined as the amount of
matter an object has
– Size does not determine mass
• Weight – the result of gravity pushing down
on you.
Mass Vs Weight
Mass Vs. Weight
Mass - the amount of matter an object has
Weight – determined by gravity
Formula = same as force
F w = m * ag
Fw= Force of weight (Newtons)
m = mass (Kilograms)
ag = acceleration due to gravity=9.8 (meters/sec 2)
Newton’s 3rd Law
• For every action there is an equal and
opposite reaction
When one object exerts a force on another
object, the second object exerts a force of
equal strength in the opposite direction on the
first object. (Action / Reaction)