Velocity vs. Acceleration

Velocity vs. Acceleration

S8P3.  a. Analyze and interpret data to identify patterns in the relationships between speed and distance, and velocity and acceleration. (Clarification statement: Students should be able to analyze motion graphs, but students should not be expected to calculate velocity or acceleration.)

Acceleration

• Acceleration is the rate at which velocity changes. So, an object accelerates if its speed, its direction, or both changes (units is meters per second squared).

Positive Acceleration

• An increase in velocity is commonly called positive acceleration.

Negative Acceleration

• A decrease in velocity is commonly called negative acceleration.

No Acceleration

When an object’s velocity is at a constant speed (no change in speed or direction), the object has zero acceleration.

Constant Velocity vs. Constant Acceleration

- Constant acceleration should not be confused with constant velocity. If an object's velocity changes the object is accelerating.

- An object with a constant velocity is not accelerating, no matter how fast it might be moving.

Distance-Time Graphs

The three graphs to the right show velocity, or changes in position over time. The first graph show the velocity of the object is increasing. The object is accelerating. The second graph, the velocity of the object is decreasing over time. This object is also accelerating, but its acceleration is negative.

Distance-Time Graph

The third graph, the velocity of the object does not change. The third object is not accelerating.

Velocity-Time Graphs

The graphs to the right represent the motion of the same three objects. These three graphs show acceleration, or change in velocity over time. In the first graph, the object's velocity is increasing, and acceleration is positive. In the second graph, velocity is decreasing, and acceleration is negative.

Velocity-Time Graphs

In the third graph, the object's velocity is constant, so the object is not accelerating.

Is acceleration occurring in the situations below? Why? or Why not?

• You are riding your bike at 9 km/h. Ten minutes later, your speed is 6 km/h.

  
  

  You ride your bike in a straight line at a constant speed of 10 km/h.

• You ride your bike around the block at a constant speed of 11 km/h.

• You ride your bike in a straight line at a constant speed of 10 km/h.

Acceleration Scenarios Answers:

• 1. Acceleration occurred because speed decreased.

• 2. Acceleration occurred because direction changed.

• 3. No acceleration occurred because neither speed nor direction changed.

Acceleration is not only

how much velocity changes, but

also how fast velocity changes. The faster the velocity changes, the greater the acceleration.

What are some situations in which there would be faster changes in velocity?

Possible Answers

Roller coaster, race cars racing, etc.

How does the increase in an object’s mass affect its acceleration?

If an object’s mass increases, then the acceleration of the object will decrease. Why?

Answer: A larger mass means more inertia. The more inertia an object has, the harder it is to move. Or the greater the force needed to change its motion.

A speed-tine graph can be used to find acceleration.

Other Examples