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# Acceleration Facts Acceleration is a way that we measure how fast or the speed of something. Whether it’s a bike or a car, you know that when you press the gas pedal or start pedaling faster on your bike that you begin to increase your speed. The amount of increase is acceleration.

There are various things that affect acceleration. Let’s say that you were riding your bike and you stopped pedaling. You would notice that the bike is beginning to slow down. This is called deceleration. The bike is slowing down because there is friction on the tires as well as in the air and the friction slows down the acceleration process.

• One of the main causes of acceleration is gravity. Gravity will intensify or increase the acceleration causing the speed or velocity to increase.
• We know about acceleration because of the intense scientific work of two scientists: Galileo Galilei (1564-1642), from Italy, and Isaac Newton (1642-1727) from England. Both were physicists.
• Galileo watched objects as they rolled down an ‘inclination’ or hill. He created mathematical equations that demonstrated how the speed of the objects increased as they continued to roll down. The equations that he came up with were the first ideas of what is called ‘accelerated motion’.

Isaac Newton studied the results that Galileo came up with and continued observations and calculations. He came up with the idea that the speed (velocity) of an object changes when a specific force acts upon the object. An example of his calculations would be a baseball rolling down an inclined plank and then someone coming along and hitting it with a stick. The speed increases due to being hit. Newton discovered the relationship between acceleration and force and has become one of the main concepts of physics in the modern world today.

The idea of ‘linear acceleration’ is what happened in the example of the ball rolling down an inclined plank and then being hit to increase the speed or velocity.

There are two factors that acceleration depends upon direction and velocity. If you are in a car going at a constant speed but it changes direction it is also accelerating. This also relates to the same car going around a curve in the road. The speed remains constant but the car is accelerating. This is referred to as ‘circular acceleration’.

A typical example of circular acceleration might be to consider the motion of the moon as it travels around the earth. Its orbit travels at a constant speed but at the same time, it is falling towards the earth due to the Earth’s gravity. The gravity acts on the moon to change the direction that it is traveling but doesn’t change the velocity.

The effect that gravity has on all objects is pretty powerful. Imagine the amount of ‘pull’ that gravity has on a rocket that needs to blast off into space. There needs to be enough fuel in the rocket tanks to allow it to pull away from the earth and increase its speed so that it can make its way out of the atmosphere.

• In the case of a rocket, it is battling both gravity and the air around the ship to increase its acceleration. The burning fuel creates enough energy or ‘force’ to allow the rocket to pull away from the earth.
• Can you think of any other examples of acceleration? Of linear acceleration? Of circular acceleration?
• How would a windy day affect riding your bike down a hill? What would the wind be called as an effect on acceleration?

### Important words to know:

Force, acceleration, gravity, linear acceleration, circular acceleration, velocity

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Facts for Kids