1. Lecture 4 Motion and Velocity Ozgur Unal
NIS – PHYSICAL SCIENCE
Lecture 4
Motion and Velocity
Ozgur Unal

2. As the ball rolls down, what quantity of the ball changes?
Motion
As the ball rolls down, what quantity of the ball changes?
Motion is a change in position.
To measure the position of an object, a reference frame must be chosen.
The position of the ball measured depends on the reference frame chosen.
Motion is relative.
The speed you measure depends on the reference frame.

3. Motion Distance vs Displacement: Distance is a scalar.
Distance is the length of path traveled by an object.
Displacement is the change in position. It includes distance and direction.
Distance is a scalar.
Displacement is a vector.
Scalars have magnitude only,
whereas vectors have both magnitude and direction.
Scalar: mass, volume money etc..
Vector: Displacement, force etc.

4. How fast do these sprinters run? www.youtube.com/watch?v=3nbjhpcZ9_g
Speed
How fast do these sprinters run?
Speed is the distance an object travels per unit time. It tells you how fast an object moves.
The unit of speed is m/s in SI.
Usually, the speed of an object changes as it moves from one place to another.
Instantaneous speed is the speed at a single instant of time.

5. Average Speed
Since the speed of an object changes from place to place, it is useful to define average speed of the motion.
Average speed is the total distance traveled divided by the total time.
average speed = total distance / total time
An elevator travels a distance of 220m from the first floor to the 60th floor in 27.5s. What is the elevator’s average speed?
Total distance traveled: d = 220 m
Total time: t = 27.5 s
v = d/t = 220m/27.5s = 8m/s

6. Velocity Imagine a tornado in your neighborhood.
You know the speed of the tornado and
you know how far it is.
What else do you need to know to make
sure that you are safe?
The velocity of an object is the speed of the object and its direction of motion.
Even if the speed of an object is constant, its velocity can be changing. Example: Circular motion
You HAVE TO specify the magnitude and the direction of velocity.
Velocity is a vector.

7. Lecture 5 Graphing Motion August 26, 2010 Ozgur Unal
NIS – PHYSICAL SCIENCE
Lecture 5
Graphing Motion
August 26, 2010
Ozgur Unal

8. Graphing Motion
The motion of a moving object can be shown on a distance-time graph.
Distance-time graphs are line graphs with time on the x-axis.
Distance is shown on the y-axis.
If an object moves with constant velocity, how do you think its distance-time graph will be?
The graph should have a straight
line with a positive slope.

9. Distance-Time Graphs
If an object is at rest (i.e. not moving), how will its distance-time graph be?
If an object is not moving
(zero speed), there will be a
horizontal line on distance-time
graph.
Consider 3 objects starting their motion at the same point with different speeds in the same direction.
Which object moves the fastest?
Which object moves the slowest?

10. Distance-Time Graphs How about these distance-time graph?
Is the speed uniform (constant)?
If not, how is it changing in each graph?

11. Lecture 6 Acceleration August 27, 2010 Ozgur Unal
NIS – PHYSICAL SCIENCE
Lecture 6
Acceleration
August 27, 2010
Ozgur Unal

12. Acceleration Imagine a car at rest at the traffic lights.
When it turns green, the car starts moving and the velocity of the car increases.
Acceleration is the change in velocity divided by the time for that change to occur.
Is acceleration a vector?
Yes. Since acceleration is the change in VELOCITY per unit time, it has a direction and a magnitude.

13. Consider an object in circular motion. Is that object accelerating?
Acceleration
A car speeding up on a highway is accelerating.
A vehicle slowing down at an instersection is decelerating.
Consider an object in circular motion.
Is that object accelerating?
Yes. Since the direction of velocity is
continuously changing, it is accelerating.

14. Calculating Acceleration
The following equation is used to calculate the average acceleration of an object moving in 1-D.
average acceleration = (vf - vi)/(tf - ti)
What is the unit of acceleration?
Example: A ball is dropped from a cliff and reaches a speed of 29.4 m/s after 3.0 s. What is the ball’s average acceleration?

15. Positive and Negative Accelerations
Calculating Positive Acceleration: If an object is speeding up, its acceleration is positive. This is because the size of the final velocity is always greater than the size of the initial velocity.
Calculating Negative Acceleration: If an object is slowing down, its acceleration is negative. This is because the size of the final velocity is always smaller than the size of the initial velocity.

16. Speed-Time Graphs
The slope of a speed-time graph can be used to find the acceleration of an object.