Transcript Newton`s 1st Law of Motion

Inertia and Newton’s
of Motion
Chapter 2.2 + 2.5
st
1
Law
Inertia
• Galileo found that a force is required to start and object
moving, but once moving, no force is required to keep it
moving.
• The tendency of objects that are moving to stay moving
and objects at rest to stay at rest is called Inertia
Newton’s First Law of Motion
• Sir Isaac Newton (1642 – 1727) was able to state rules
describing the effect of forces on motion of objects that are
still true today.
• These rules are known as:
Newton’s Laws of Motion
• Newton’s First Law of Motion is also called
The Law of Inertia
Newton’s First Law of Motion
• An object moving at a constant velocity keeps
moving at that velocity unless a net force acts on it.
• If an object is at rest, it will stay at rest, unless a
net force acts on it.
• If an object is in motion, it will stay in motion,
unless a net force acts on it.
What Happens in a Crash?
• Newton’s Law First Law of Motion
• If you are traveling at 50 kilometers per hour and you hit
a tree…
What Happens in a Crash?
• If you are not wearing your seatbelt…
• The car is stopped by the tree and you continue to move
forward at a speed of 50 kilometers per hour until you hit
the dashboard, steering wheel, windshield, etc.
• You would hit at the same speed you would reach if you
fell from a three-story building.
What Happens in a Crash?
• The seatbelt loosens a little upon impact and will hold you.
• If you are wearing your seatbelt…
• This allows your body to be slowed down gradually and
decreases the unbalanced force placed on your body.
• The seatbelt could also save you from being thrown
outside the car.
Speed and Velocity
Chapter 2.3 + 2.4
Speed
• Galileo was the first to measure speed by conidering the
distance covered and the time it takes.
• He defined speed as the distance covered per unit of
time.
– The term per means “divided by”
• The equation we use to define speed is:
Speed =
Distance
Time
• Suppose you ran 2 km in 10
min.
– What is your rate?
S = d/t
S= 2 km /10 min.
S= 0.2 km/min.
Remember the units!!!
Constant Speed…
• What does constant mean?
• If you are driving on the highway and you set your
cruise control, you are driving at a constant speed.
• What would a constant speed graph look like?
Constant Speed Graph
Constant Speed
• Now think about how an object’s distance changes
over time when moving at a constant speed…
Two Objects with Constant Speed
• Which one is going faster?
• A steeper gradient indicates
a larger distance moved in a
given time. In other words,
higher speed.
• This means the object
represented by the yellow
line has a greater speed.
Do you always go the same speed?
• No! Most of the time
you are increasing
speed, decreasing
speed, or stopping
completely!
• Think about driving
a car or riding a
bike!
What is average speed?
• Total distance traveled over the total time of travel
• How do you find an average?
- Take the total distance traveled
and divide it by the total time of
travel
What is average speed?
• How do you find an average?
• Average speed is the total distance traveled over
the total time
• Avg. Speed = Total d / Total t
• Avg S = Td/Tt
What is Instantaneous speed?
• What does a speedometer in a car do?
– It shows how fast a car is going at one point in time or at
one instant.
• Instantaneous speed is the speed at a given point
in time.
What is Velocity?
• Speed is how fast something is moving.
• Velocity is how fast something is moving and in
what direction it is moving.
• Why is this important?
– Hurricanes
– Airplanes
Speed or Velocity?
• If a car is going
around a racetrack,
its speed may be
constant (the same),
but its velocity is
changing because it
is changing
direction.
Speed or Velocity?
• Escalators have the
same speed
(constant), but have
different velocities
because they are
going in different
directions.
Elements
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