MotionSpeedVelocity-and-Acceleration-1.ppt

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1. Motion, Speed, Motion, Speed,
Velocity and Velocity and
AccelerationAcceleration

2. MotionMotion
►MotionMotion – an object’s change in position – an object’s change in position
relative to a reference pointrelative to a reference point

3. Reference PointReference Point
►The Earth’s surface is used as a common The Earth’s surface is used as a common
reference pointreference point
►A moving object can be used as a A moving object can be used as a
reference point as wellreference point as well

4. SpeedSpeed
►SpeedSpeed is the distance traveled divided by is the distance traveled divided by
the time interval during which the motion the time interval during which the motion
occurredoccurred
►Normally, objects do not travel at a Normally, objects do not travel at a
constant speedconstant speed
►Average Speed - Average Speed - total distancetotal distance
total timetotal time

5. SpeedSpeed
1.1.If a car travels 400 m in 20s how fast is it If a car travels 400 m in 20s how fast is it
going?going?
2. You need to get to class, 200m away and
you can only walk in the hallways about 1.5
m/s. How much time will it take to get to
your class?

6. Which Distance?Which Distance?
►Farmer Jones drives 6 miles down a straight Farmer Jones drives 6 miles down a straight
road. She turns around and drives 4 miles back. road. She turns around and drives 4 miles back.
What was her average speed for this trip if it What was her average speed for this trip if it
took 1 hour?took 1 hour?

  
                                          
 
             

7. Your answer to this problem depends on Your answer to this problem depends on
your interpretation of "distance traveled". your interpretation of "distance traveled".
You could say:You could say:
►The The total distancetotal distance traveled by Farmer Jones is traveled by Farmer Jones is
10 miles. Therefore her average speed is 10 10 miles. Therefore her average speed is 10
mi/hr. mi/hr.
►The The net distancenet distance traveled by Farmer Jones is 2 traveled by Farmer Jones is 2
miles. Therefore, her average speed is 2 mi/hr. miles. Therefore, her average speed is 2 mi/hr.
►There are good reasons to use either There are good reasons to use either
interpretation - it's mostly a matter of interpretation - it's mostly a matter of
preference. We will interpret "distance preference. We will interpret "distance
traveled" to be traveled" to be net distance (net distance (also calledalso called
displacement). displacement). Farmer Jones' average speed Farmer Jones' average speed
was 2 mi/hr.was 2 mi/hr.

8. VelocityVelocity
►VelocityVelocity is the speed of an object in is the speed of an object in
a particular directiona particular direction
►Imagine two birds leave the same Imagine two birds leave the same
tree at the same time. The both fly tree at the same time. The both fly
at 10km/hr for 5 minutes. Why don’t at 10km/hr for 5 minutes. Why don’t
they end up at the same place?they end up at the same place?

10. VelocityVelocity
►VelocityVelocity appears to be very similar to appears to be very similar to
speed, however, when describing the speed, however, when describing the
velocity of an object you need to velocity of an object you need to
provide a magnitude and a directionprovide a magnitude and a direction
►MagnitudeMagnitude – the speed of the object – the speed of the object
►DirectionDirection – the direction the object is – the direction the object is
movingmoving

11. VelocityVelocity
►Ex) A bus has a velocity of 35miles/hr Ex) A bus has a velocity of 35miles/hr
heading westheading west

12. Resultant VelocityResultant Velocity
►An object can have a resultant velocity if it An object can have a resultant velocity if it
is experiencing more than one motion.is experiencing more than one motion.
►For example if a person walks down the For example if a person walks down the
center of a bus while it is in motion there center of a bus while it is in motion there
are two velocities occurring.are two velocities occurring.
1. The movement of the bus1. The movement of the bus
2. The movement of the person inside the 2. The movement of the person inside the
busbus

13. ExampleExample
15 m/s
+ 1 m/s = 14 m/s

14. ExampleExample
15 m/s
+ =
1 m/s 16 m/s

15. AccelerationAcceleration
►AccelerationAcceleration is the rate at which velocity is the rate at which velocity
changes over timechanges over time
An object accelerates if its speed, direction, or An object accelerates if its speed, direction, or
both changeboth change
►Average acceleration =
final velocity – starting velocity
time it takes to change velocity

16. AccelerationAcceleration
►ExampleExample
A car on the highway is traveling 55 mi/hr A car on the highway is traveling 55 mi/hr
and it passes another car. In order to pass, and it passes another car. In order to pass,
the car has to accelerate to 65 mi/hr. The car the car has to accelerate to 65 mi/hr. The car
reaches this velocity 40 seconds later. What reaches this velocity 40 seconds later. What
is the average acceleration of the car?is the average acceleration of the car?

17. Acceleration and VelocityAcceleration and Velocity
►As velocity As velocity increasesincreases, so does acceleration, so does acceleration
►As velocity As velocity decreasesdecreases, so does acceleration, so does acceleration
►When direction changes, so does accelerationWhen direction changes, so does acceleration
►When there is a When there is a constant velocityconstant velocity, there is , there is
no accelerationno acceleration