History for Kids Geography for kids Science for kids Kids Educational Site and Search Study and Homework for kids Sports Games
advertisement

Science >> Physics for Kids

Physics for Kids

Acceleration

When we discussed velocity and speed, we assumed a constant velocity. However, this is rarely the case in the real world. In the real world the velocity of an object in motion is often changing.

What is acceleration?

Acceleration is the measurement of change in an object's velocity. When you press down on the gas pedal in a car, the car surges forward going faster and faster. This change in velocity is acceleration.

The equation for calculating acceleration is:

Acceleration = (change in velocity)/(change in time)
or
a = Δv ÷ Δt

How to Measure Acceleration

The standard unit of measurement for acceleration is meters per second squared or m/s2. You can calculate this from the above formula where velocity is meters per second and time is in seconds.

Acceleration is a Vector

In physics acceleration not only has a magnitude (which is the m/s2 number we discussed above), but also has a direction. This makes acceleration a vector.

Force and Acceleration

Newton's second law of motion states that the force on an object equals the mass times the acceleration. This is written in the following equation:

Force = mass * acceleration
or
F = ma

We can use this formula to also figure out the acceleration if we know the mass and force on an object. This formula is:

acceleration = force/mass
or
a = F/m

Constant Acceleration

When an object is changing velocity by a constant amount over time, this is called constant acceleration. An object with constant positive acceleration will be going faster and faster. Its velocity will be increasing constantly.

Interval
1st second
2nd second
3rd second
Acceleration
5 m/s2
5 m/s2
5 m/s2
Velocity
10 m/s
15 m/s
20 m/s
An example of constant acceleration of 5 m/s2.


Free Fall: A Type of Acceleration

One example of constant acceleration is an object in free fall. During free fall, gravity applies a constant force on the object causing a constant increase in velocity. If you were to measure the distance an object fell, each second it would fall further because it is constantly picking up speed.

Note: In the real world there would be the additional force of air friction on the object. At some point the object would reach "terminal velocity". This means that it would no longer accelerate and the speed of the fall would stay the same. The terminal velocity of a skydiver falling face down is around 122 miles per hour.

Average Acceleration

The average acceleration is the total change in velocity divided by the total time. This can be found using the equation a = Δv ÷ Δt.

For example, if the velocity of an object changes from 20 m/s to 50 m/s over the course of 5 seconds the average acceleration would be:

a = (50 m/s - 20 m/s) ÷ 5s
a = 30 ms ÷ 5s
a = 6 m/s2

Deceleration or Negative Acceleration

When the velocity of an object decreases (slows down) this is called deceleration. It may also be represented by a negative acceleration. This means the direction or vector of the acceleration is pointing in the opposite direction of the movement of the object.

For example, if the velocity of an object changes from 40 m/s to 10 m/s over a time interval of 2 seconds the average acceleration would be:

a = (10 m/s - 40 m/s) ÷ 2s
a = -30 ms ÷ 2s
a = -15 m/s2
This could also be called a deceleration of 15 m/s2.


More Physics Subjects on Motion, Work, and Energy

Motion
Scalars and Vectors
Vector Math
Mass and Weight
Force
Speed and Velocity
Acceleration
Gravity
Friction
Laws of Motion
Simple Machines
Glossary of Motion Terms
Work and Energy
Energy
Kinetic Energy
Potential Energy
Work
Power
Momentum and Collisions
Pressure
Heat
Temperature



Science >> Physics for Kids

Kid's Poll



More polls











Privacy Policy

Kids Games  History for Kids  Homework Help  Science  Geography for Kids 

About Ducksters  Link to Ducksters  Teachers 

Last updated: This site is a product of TSI (Technological Solutions, Inc.), Copyright 2014, All Rights Reserved. By using this site you agree to the Terms of Use.


To cite this article using MLA style citation: