Transcript Speed = Distance/Time

Lesson 18
OBJECTIVES
• Describe the force exerted by a batterypowered fan car.
• Describe the motion of a fan car
• Determine the effect of a constant force on
the speed of a fan car
• Calculate a fan car’s average speed at
different times as it moves along a path
Getting Started
• What does the term “average speed”
mean?
• Average speed refers to the distance an
objects moves in a given time.
• How do you calculate it?
• Average speed = Distance
•
Time
Getting Started
• A car travels 100 meters (m) in 2
seconds. What is its speed?
• Speed = Distance/Time
• Speed = 100 m/ 2 seconds
• Speed = 50 m/s
Getting Started
• A car travels 100 meters (m) in 2
seconds. What is its speed?
• Speed = Distance/Time
• Speed = 100 m/ 2 seconds
• Speed = 50 m/s
Getting Started
• A jogger runs 50 meters in 25 seconds.
What is the jogger’s speed?
• Speed = Distance/ Time
• Speed = 50 m / 25 s
• Speed = 2 m/s
Vocabulary – Lesson 18
• Speed
• The rate at which an object changes its position over
time or how fast something is moving
•
distance traveled
time traveled
Acceleration
• When unbalanced forces act on an object, the object
speeds up or slows down. The rate at which speed
changes
Vocabulary
• Average Speed
• The distance an object moves divided by the
time it takes to move that distance.
• Speed = Distance / Time
• Rate
• A measure of the way a quantity changes over
time.
Vocabulary
• Inertia
• The tendency for objects to maintain their
motion when no forces act on them
• Balanced Force
• Action of equal forces on an object in
opposite directions (cancel each other out
so net force is zero)
Vocabulary
• Unbalanced Force
• Forces that produce a non zero net force,
which changes an object’s motion in the
direction of the greater force.
Vocabulary – Lesson 18
• Newton’s first law of motion
– (inertia) –An object at rest will remain at rest,
and an object moving at a constant velocity
will continue moving at a constant velocity,
unless acted on by an unbalanced force
Vocabulary
• Newton’s Second Law of Motion
• - Force = mass x acceleration
• -An object acted upon by a force, will
accelerate in the direction of that force.
• Acceleration depends on the mass of the
object and the force action on the object.
Vocabulary
• Newton’s Third Law of Motion
• -For every action, there is an equal but
opposite reaction.
• If one object exerts a force on another
object, then the second object exerts a
force of equal strength in the opposite
direction on the first.
Notes
• Speed is the rate at which an object
changes its position over time and is
calculated as:
• Speed = Distance/Time
Notes
• Average speed is calculated as
Total distance traveled / Total time
traveled
An object that moves with changing speed is
accelerating.
Acceleration is the rate at which the speed
changes.
Notes
When an unbalanced force acts on an
object, the object will accelerate, or
change its speed.
The acceleration can be a change in speed
OR a change in direction of the motion of
the cars.
Notes
The greater the unbalanced force, the
greater the acceleration.
This is summarized by Newton’s 2nd Law of
motion which states :
Force = Mass x Acceleration
Notes
• If unbalanced force is parallel to motion of
an object, only the speed changes
• If force is in same direction of the emotion,
the speed will increase.
• If force is in opposite direction, the speed
will decrease.
Notes
• If a constant unbalanced force acts on an
object, it will have a constant acceleration,
so there will be a steady change in speed
of the object.
Notes
Inertia is the tendency for objects to
maintain their motion when no forces act
on them. (Newton’s 1st Law of Motion)
This is why if you push something, it will
keep moving a small amount of time. The
force of friction will cause it to stop.
Notes
The motion of the car can be described in
transformations:
Your hand pushes the car and gives it KE.
After you push, the car still has KE but
friction works against the motion and
eventually changes the KE into heat.
Notes
As the car loses KE, it slows down.
When all KE has been converted to heat,
the car stops.
Notes
When the fan is used, the fan pushes air
through the blades. The air pushes on the
fan that is attached to the car.
The air goes in one direction, the car in the
opposite direction.
This is an example of Newton’s 3rd Law of
Motion which states “For every action,
there is an equal and opposite reaction”.
Notes
When the fan is on, a constant unbalanced
force accelerates the car forward and the
car moves with increasing speed.
Lesson 18
Question – Lesson 18
• How does the speed of a fan car change
at .4 m intervals across a distance of 2
meters?
• Lesson 18
• If _________________,then __________
because _________________.
SAFETY
• KEEP YOUR FINGERS AWAY FROM
THE MOVING FAN BLADES!!!!
• Lesson 18
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Materials
1.
2.
3.
• Lesson 18
Time and Distance Data for the Fan Car
Distance Position
Interval
(m)
Time
(s)
Trial 1
1
0.0 - 0.4
2
0.4 – 0.8
3
0.8 – 1.2
4
1.2 – 1.6
5
L 18
1.6 – 2.0
Trial 2
Trial 3
Avg.
Speed
(m/s)
Average
• Lesson 18