1. Definition:
Acceleration is the rate at which an object changes its velocity. If the object moves in a stright line and changes the same rate at the same time, this is a constant acceleration. Acceleration is a vector.
2. Calculate the magnitude of acceleration:
If a car is traveling in a straight way, its velocity changes according to the following table. What is the acceleration of the car according to its definition?
| Time(S) | Velocity (m/s) |
| 0 | 0 |
| 1 | 20 |
| 2 | 40 |
| 3 | 60 |
| 4 | 80 |
Pick any two points to calculate the magnitude of the acceleration:
(40m/s - 20m/s)/(2s - 1s) = 20m/s/s
If we use:
a: Acceleration
Vi: Initial Velocity
Vf: Final Velocity
ti: Initial Velocity
tf: Final Velocity
From here, we can conclude the formula of the acceleration: a = (Vf - Vi)/(tf - ti)
3. The unit of the parameters:
t: second (s)
V: meter per second (m/s)
a: meter per second per second (m/s/s)
or meter per second square. (m/s2)
4. Direction of the acceleration: look at the picture below:
5. Conclusion:
When an object changes either its magnitude or its direction, the acceleration changes.
The direction of the acceleration is the same direction of the object's motion when an object is speeding up.
The direction of the acceleration is in the opposite direction of the object's motion when an object is slowing down.
This is the Rule of Thumb.
6. Check your understanding:
- Which has great acceleration when moving is a straight line, a car that increases its speed from 50km/h to 60km/h, or a bicycle that goes from zero to 10km/h in the same time? Explain your answer.
- What is the acceleration of a car that travels in a straight line at a constant speed of 100km/h?
- A car starts from rest and accelerates uniformly over a time of 5.21s for a distance of 110m. What is the magnitude of acceleration of the car.
7. What year are you taking now?
