Acceleration
Remember Velocity? Velocity is a description of the speed and direction of motion. Velocity is a vector, which means that it is a quantity with both a magnitude and a direction. Ex. Velocity = 4 m/s West Speed = 4 m/s (no direction given)
Acceleration The rate at which velocity changes is called acceleration. Acceleration can be described as changes in speed, changes in direction, or changes in both. The units for acceleration are meters per second per second (m/sec2)
Acceleration caused by Changes in Speed Most people think of acceleration as “going faster” However, changes in speed can be positive (increasing) or negative (decreasing).
Free Fall Free Fall is an example of acceleration due to a change in speed. The movement of the object towards Earth solely because of gravity. Objects near Earth accelerate downward at a rate of 9.8 m/sec2
For each second that an object is in free fall, its velocity increases by 9.8 m/s. A tandem skydiver free falling from a plane at 13,500 feet would free fall for about a minute and could reach a maximum speed of around 120 mph
Acceleration Caused by Changes in Direction A carousel travels at a constant speed the whole ride but there is an acceleration because you change direction as you go around the carousel.
Acceleration caused by changes in Speed in Direction Roller Coasters are examples of acceleration due to both changes in speed and direction.
Constant Acceleration Constant acceleration is a steady change in velocity. The velocity of an object changes by the same amount each second.
Example of Constant Acceleration An airplane during takeoff may have constant acceleration. The direction stays the same but the speed is increasing.
Calculating Acceleration Formula for acceleration in a straight line motion: Acceleration = (Vf – Vi) T
If the velocity increases you will have a positive answer from the formula. This means a positive acceleration. If the velocity decreases, you will have a negative answer from the formula. This means a negative acceleration or deceleration.
Graphs of Accelerated Motion
Remember, distance vs. time graphs show changes in speed Remember, distance vs. time graphs show changes in speed. A change in speed is acceleration!