Accelerated MotionChapter 3.1

Page 57

The most important thing to notice in motion diagrams is the distance between successive positions!

If the change in position gets larger, the object is speeding up.

If the change in position gets smaller, the object is slowing down.

Changing Velocity

Motion Diagram…

There are two major indicators of the change in velocity in this form of the motion diagram.

1. The change in spacing of the dots2. The differences in the lengths of the velocity

vectors.

Particle-Model Motion Diagram

Particle-Model Motion Diagram

Looking at the graph on the next slide, the slope is 5.00m/s. This means that every second, the velocity increases by 5.00m/s.

The rate at which an object’s velocity changes is called acceleration.

When velocity changes at a constant acceleration.

Velocity-Time Graphs

Velocity-Time Graph

Average Acceleration – the change in velocity during some measurable time interval divided by that time interval. Measured in m/s2

Instantaneous Acceleration – can be found by drawing a tangent line on the velocity-time graph at the point of time in which you are interested.

Average and Instantaneous Acceleration

For a motion diagram to give a full picture of an object’s movement, it should contain acceleration.

To determine length and direction of an average acceleration vector, subtract two consecutive velocity vectors and divide by time interval.

Displaying Acceleration on a Motion Diagram

Vf - Vi = Vf + (-Vi)

Positive and Negative AccelerationRead page 61

In the first and third situations when the object is speeding up, the velocity and acceleration vectors point in the same directions.

In the other situations the acceleration vector is in the opposite direction from the velocity vector; therefore, the object is slowing down.

Looking at page. 61

When the object’s acceleration is in the same direction as the velocity, the object’s speed increases.

When they are in opposite directions, the speed decreases.

Velocity and direction of acceleration are needed to determine whether it is speeding up or slowing down.

Soooo….

Determining Acceleration from a v-t Graph…pg. 62

Calculating Acceleration

Acceleration and Velocity Comparison

Acceleration Rate of change Time rate of change of

velocity Have average and

instantaneous forms Area under

acceleration-time graph is equal to the object’s velocity.

Velocity Rate of change Rate of change in

position Have average and

instantaneous forms Area under a velocity-

time graph is equal to the object’s displacement.