Download Interpret The Graph Below

Forces & Motion
Review
Describe Speed
Describe Speed
• A way to describe motion
– Average speed - Rate of motion calculated by dividing
the distance traveled by the amount of time it takes to
travel that distance
– Constant speed - Speed that does not change
– Instantaneous speed - Speed of an object at any
given time
What is the formula used to
calculate speed?
What is the formula for
calculating speed?
Speed is calculated by dividing distance
by time –
Calculate This Speed
A football field is about 100 m long. If it
takes a person 20 seconds to run its
length, how fast was the football player
running?
Calculate this Speed:
A football field is about 100 m long. If it
takes a person 20 seconds to run its
length, how fast was the football player
running?
Speed = Distance ÷ Time
Speed = 100 m ÷ 20 s
Speed = 5m/s
Remember
to include
the UNITS!!
Distinguish Between Speed
& Velocity
Describe Acceleration
Describe Acceleration
• A change in velocity – which may be:
– A change in speed
•
•
•
•
Starting
Stopping
Speeding up
Slowing down
– A change in direction
• Acceleration is caused by unbalanced
forces
More
Acceleration
Any change in velocity
divided by the time
during which the
change occurred.
Metric Units for Acceleration
m/sec/sec OR m/sec2
Also: km/hr2
ft/sec2
Acceleration
Acceleration = change in velocity over time
a = rv OR a = vf - vi
t
t
vf = final velocity & vi = initial velocity
You can solve for t, vf, or vi:
t = v f - vi
a
vf = at +vi
vi =vf – (at)
Describe Acceleration
Deceleration is also called negative
acceleration - it means an object is
slowing down
When acceleration is calculated, it may be a
negative number
Interpret The Graph Below:
Interpret The Graph Below:
The graph shows
an object which
is not moving (at
rest).
The distance
stays the same
as time goes by
because it is not
moving.
Interpret The Graph Below:
Interpret The Graph Below:
The graph shows
that the objects
distance increases
as time passes.
The object is moving
and so it has
velocity.
The straight line
shows it is a
constant (not
changing).
Interpret The Graph Below:
Interpret The Graph Below:
Just like the
previous
graph, this
graph shows
an object
moving with
constant
velocity
Explain Balanced Forces
• When all the forces acting on an object
balance each other
• Balanced forces do not cause a change in
motion
Interpret The Graph Below:
Interpret The Graph Below:
In the first part of
the graph the object
is moving with
constant velocity.
In the second part of
the graph the object
is at rest (not
moving).
In the third part the
object is again
moving with
constant velocity.
Interpret The Graph Below:
Interpret The Graph Below:
The graph shows
that the objects
velocity does not
change as time
passes.
It shows constant
velocity.
Interpret The Graph Below:
Interpret The Graph Below:
The graph shows
that the objects
velocity is
increasing as time
passes – it is
accelerating.
The straight line
shows that it is
constant
acceleration.
Interpret The Graph Below:
Questions
1. Which runner
won the race?
Explain your
answer.
2. Which runner
stopped for a rest?
Explain your
answer.
3. How long was the
stop? Explain
your answer.
The graph above shows three runners who ran a 100-meter race.
4. How long did Bob take to complete the race? Explain your answer.
5. Calculate Albert’s average speed. (Figure the distance and time first!)
Questions
The graph below shows how the speed of a bus
changes during part of a journey.
Choose the correct words from
the following list to describe
the motion during each
segment of the journey to fill
in the blanks:
• Accelerating
• Decelerating
• Constant speed
• At rest
Segment O-A: The bus is _____. Its speed changes from 0 to 10 m/s in 5 seconds.
Segment A-B: The bus is moving at a _____ of 10 m/s for 5 seconds.
Segment B-C: The bus is _____. It is slowing down from 10 m/s to rest in 3 seconds.
Segment C-D: The bus is _____. It has stopped.
Segment D-E: The bus is _____. It is gradually increasing speed.
Explain Balanced Forces
Explain Balanced Forces
• When all the forces acting on an object
balance each other
• Balanced forces do not cause a change in
motion
Describe Friction
Describe Friction
• Force that resists motion between two
touching surfaces
• Acts in the opposite direction of the
object’s motion
• Produces heat
Explain Inertia
Explain Inertia
• Moving objects tend to continue moving unless
acted upon by an unbalanced force
• Objects at rest tend to stay at rest unless acted
upon by an unbalanced force
• The more mass an object has, the more inertia it
has
– More massive objects are harder to start moving and
stop moving
– Smaller objects are easier to start and stop moving
More
Explain Inertia
Newton’s First Law on Motion describes the
idea of inertia
• An object at rest or in constant motion is
acted upon by balanced forces – an
unbalanced force will change the motion
• Acceleration of an object at rest or in
constant motion is 0 m/s/s (no motion)
Explain Newton’s First Law
of Motion
Explain Newton’s First Law of
Motion
• Describes the idea of inertia
Distinguish Between Speed and
Velocity
• Speed describes distance and time
• Velocity describes distance, time, and
direction
Explain Newton’s Second Law of
Motion
Explain Newton’s Second Law of
Motion
• Describes motion created by unbalanced forces
• Mass and acceleration change in opposite ways
– The more mass an object has, the more force it
take to accelerate the object, the slower it
accelerates
– The less mass an object has, the less force it
take to accelerate the object, the faster it
accelerates
More
Explain Newton’s Second Law of
Motion
Explain Newton’s Third Law
of Motion
Explain Newton’s Third Law of
Motion
• Describes why forces act in pairs
• For every action there is an equal and opposite
reaction
• Action and reaction forces are equal forces
acting in opposite directions on different objects
Explain Newton’s Third Law of
Motion
How Can Forces Affect
Objects?
How Can Forces Affect Objects?
•
•
•
•
•
•
Slow them down
Speed them up
Stop them
Start them
Change their direction
Change their shape
Describe Acceleration
• A change in velocity – which may be:
– A change in speed
•
•
•
•
Starting
Stopping
Speeding up
Slowing down
– A change in direction
• Acceleration is caused by unbalanced
forces
More