topic 2-unit 01-MotionSpeedVelocity-and-Acceleration.ppt

The concept of motion in physics is one of the important topics in Classical Mechanics. Did you know that everything in the universe is always moving? Even if you are completely still, you still belong to the earth which is continuously moving about its axis and around the sun. Motion means a change in the position of an object with reference to time.

1. Mechanics

2. Motion–an object’s change in position relative to a
reference point

3. The Earth’s surface is used as a common reference
point
A moving object can be used as a reference point as
well

4. Vector-quantity with both magnitude (size) and direction
Scalar -quantity with magnitude only
Vectors:
•Displacement
•Velocity
•Acceleration
•Momentum
•Force
Scalars:
•Distance
•Speed
•Time
•Mass
•Energy

5. 

6. Ex:
Farmer Jones drives 6 km down a straight road. She
turns around and drives 4 km back. What was her
average speed for this trip if it took 1 hour?
6 km
4 km

7. The net distancetraveled by Farmer Jones is 2 km. Therefore,
her average speed is 2 kmh
-1
There are good reasons to use either interpretation -it's mostly a
matter of preference. We will interpret "distance traveled" to be
net distance(also calleddisplacement).Farmer Jones' average
speed was 2 kmh
-1
6-4 =2 km
6 km
4 km
The total distancetraveled by Farmer Jones is 10 km.
Therefore her average speed is 10 kmh
-1

8. 

9. Velocityappears to be very similar to speed, however,
when describing the velocity of an object you need to
provide a magnitude and a direction
Magnitude–the speed of the object
Direction–the direction the object is moving

10. Example
Imagineapersonmovingrapidly-onestepforwardandonestep
back-alwaysreturningtotheoriginalstartingposition.
Whilethismightresultinafrenzyofactivity,itwouldresultina
zerovelocity.Becausethepersonalwaysreturnstotheoriginal
position,themotionwouldneverresultinachangeinposition.
Sincevelocityisdefinedastherateatwhichthepositionchanges,
thismotionresultsinzerovelocity.

11. Ex:
A bus has a velocity of 35kmh
-1
heading west

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

13. 15 ms
-1
+ 1 ms
-1 = 14 ms
-1

14. 15 ms
-1
+ =
1 ms
-1
16 ms
-1

15. Exercise
Youareonabustraveling25m/sforward.Yougotothe
backofthebustovisityourfriendyouarewalkingata
speedof3m/s.Whatisyourresultantvelocity?
Answer
=25-3
=22 m/s

16. Accelerationis the rate at which velocity changes over
time
◦An object accelerates if its speed, direction, or both change
Average acceleration =
final velocity –starting velocity
time it takes to change velocity

17. Example
◦A car on the highway is traveling 55 kmh
-1
and it passes
another car. In order to pass, the car has to accelerate to
65 kmh
-1
. The car reaches this velocity 40 seconds
later. What is the average acceleration of the car?
Answer:
1
st
method
Acceleration =(final velocity-initial velocity)/ time
=(65 km/h-55km/h)/(40/3600)h
=900 km/h

18. 2
nd
method: you can convert the velocity (km/h to m/s) and then find
the answer using acceleration equation
Difference of velocity =(65-55) km/h convert to m/s
Convert 10 kmh
-1
to ms
-1
10 km x 1000 m= 2.78 ms
-1
1h 3600 s
Acceleration =(final velocity-initial velocity)/ time
=(2.78 m/s ) /40 s
=0.0695 m/s

19. As velocity increases, so does acceleration
As velocity decreases, so does acceleration
When direction changes, so does acceleration
When there is a constant velocity, there is no
acceleration

20. Q1
A car travels from point A to B in 3 hours and returns back to
point A in 5 hours. Points A and B are 150 km apart along a
straight highway. Which of the following statements most
accurately describes the motion of the car?
Please choose from one of the following options.
The average velocity is 40 km per hour.
The average speed is 37.5 km per hour.
The car travels at 50 mph for the first half and 30 mph for
the second half.
The total displacement of the trip is 300 km.

21. Exercise:
01. A car travels 10 km northwards, followed by 4 km southwards.
What is the magnitude of its distance and displacement?
02. A man traveled a total distance of 35km. His trip took 7 hours.
What was his average speed?