1. Changing speed and velocity:

2. How do you describe that a car or
object changes its speed or velocity?
• When it slows down
• When it speeds up
In what situations or places where cars happen to
change the speed?
• When it is travelling in a high way its speed increases.
• When it travels in a traffic road the speed decreases
• When it turns a curve path the car also slows down.

3. What do you call this rate of change
in velocity of the object?
• It is called acceleration.
• In formula we can write acceleration as:
• Acceleration= change in velocity
•
elapsed time
• In symbol:
• a = Δv or a = vf - vi
Δt
tf - ti

4. Vf is final velocity , vi is initial velocity
tf is final time
, ti is initial time
What is the MKS unit of acceleration?
The MKS unit of acceleration is meter per
second squared, in symbol m/s². Other unit is
the km/h²

5. Application:
• Solve the given problems:
• 1. A car on a straight level road is stopped for
a red light. On the green light, it uniformly
accelerates to a velocity of 18m/s in 3
minutes. What is its acceleration?
• A jet plane flying at 100m/s is uniformly
accelerated to a cruising speed of 150m/s in
20 minutes. What is its acceleration during
this time?

6. Reinforcement:
• Which of the following is a graph of
acceleration?
• A.
B.
C.
v
v
v
t
t
t
Answer:
All of them show a graph of acceleration.
Why?

7. • 2. How do you describe the slope of graph
A? graph B? Graph C ?
Answer:
Graph A has a positive slope
Graph B has zero slope
Graph C has negative slope
3. What does a positive slope mean? A zero
slope? A negative slope?

8. • Answer:
• Positive slope means it has a constant
acceleration, the velocity changes but at
constant rate.Constant acceleration is also called
uniformly accelerated motion.
• Zero slope means no acceleration but the car
is still moving with constant velocity.
• Negative slope means the acceleration is
constant at decreasing velocity, when the
velocity decreases its called deceleration.

9. Analyze the following graphs of
acceleration
• A.
B.
C.
v
v
v
t
t
Which graph shows constant acceleration?
Answer: All of them
Which graph shows highest or greatest
acceleration?
Answer: graph A, why?
t