Uniform and Non-uniform Motion

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# Uniform and Non-uniform Motion - PowerPoint PPT Presentation

VS. Not all things move in a consistent, “uniform” way… . Uniform and Non-uniform Motion. When a body covers equal distances in equal intervals of time then the body is said to describe uniform motion . Uniform Motion.

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## Uniform and Non-uniform Motion

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VS

Not all things move in a consistent, “uniform” way…

### Uniform and Non-uniform Motion

When a body covers equal distances in equal intervals of time then the body is said to describe uniform motion.Uniform Motion
When a body moves unequal distances in equal intervals of time or vice-versa, then the body is said to describe non-uniform motion.Non-Uniform Motion

An object travelling with non-uniform motion will:

• have different displacements during equal time intervals
• take different amounts of time to travel equal displacements
• have a continuously changing velocity
How can you tell???

A change in velocity ( ) occurs when the speed of an object changes and/or its direction of motion changes.

A change in velocity can be calculated by:

Changing velocity…

= change in velocity

= final velocity

=initial velocity

Case 1: If the change in velocity is the same sign (+, -) as the initial velocity, the speed of the object is increasing!

• e.g. A dragster has an initial velocity of 1 km/hr and a final velocity of 85 km/ hr. What is its change in velocity?
So what do these numbers mean???

The initial velocity and the change in velocity are both positive, so the car is speeding up!

Case 2: If the change in velocity is the opposite sign (+, -) of the initial velocity, the speed of the object is decreasing.

• e.g. A returning space shuttle lands with an initial speed of 500km/h before coming to a stop. What is its change in velocity?
So what do these numbers mean???

The initial velocity is positive and the change in velocity is negative, so the shuttle is slowing down !

Case 3: If the change in velocity is zero, the object is travelling with uniform motion!

So what do these numbers mean???

THE ROCKET CAR!!!

… OK… maybe not… just a cool clip!!!

Acceleration () is the rate of change in velocity.

This change in velocity can be due to a change in speed and/or a change in direction.

Two objects with the same change in velocity can have different accelerations.

This is because acceleration describes the rate at which the change in velocity occurs.

Acceleration!
Let’s think a little more about that…

Suppose both of these vehicles, starting from rest, speed up to 60 km/h. They will have the same change in velocity, but, since the dragster can get to 60 km/h faster than the old car, the dragster will have a greater acceleration.

The direction of the acceleration is the same as the direction of the change in velocity.

Acceleration that is opposite the direction of motion is sometimes called deceleration… but as of Physics 11 most teachers will refer only to acceleration!

Positive and negative Acceleration

Accelerating!

“Decelerating”!

1. A car speeding up in the forward direction

• If we designate the forward direction as positive (+), then the change in velocity is positive (+), therefore the acceleration is positive (+).
Examples of acceleration

2. A car slowing down in the forward direction.

• If we designate the forward direction as positive (+), then the change in velocity is negative (-), therefore the acceleration is negative (-).
Examples of Acceleration

3. A car speeding up in the backward direction.

• If we designate the backward direction as negative (-) then the change in velocity is negative (-).
• This means that the acceleration is negative (-) even though the car is increasing its speed. Remember positive (+) and negative (-) refer to directions.
Examples of Acceleration

4. A car slowing down in the backward direction.

• If we designate the backward direction as negative (-) then the change in velocity is positive (+).
• This means that the acceleration is positive (+) even though the car is decreasing its speed. Remember positive (+) and negative (-) refer to directions.
Examples of Acceleration