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Effect of Mass on Acceleration Due to Gravity
by Ron Kurtus (25 August 2009)
Intuitively, you would think that a heavier object would fall to the ground faster than a lighter object. However, that is not the case. All objects will fall to the ground at the same rate, no matter what their weight or mass, provided air resistance is a negligible factor.
Questions you may have include:
- What is the relationship between force and mass?
- How is acceleration constant?
- How can you prove this rule?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
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Force and mass
The force of gravity for objects relatively close to Earth is:
F = mg
where
- F is the force
- m is the mass of the object
- g is the acceleration due to gravity
What this means is that the force from the Earth's gravity is proportional to the mass of the object. Objects with greater mass feel a greater the force on them.
Acceleration is constant
However, the acceleration due to gravity, g, is the same for all objects, no matter what their mass. This means that all objects will accelerate or fall at the same rate, provided they are not affected by air resistance.
Balls of different mass fall at the same rate
Dropping two objects of different mass from exactly the same height and exactly the same time will result in them falling at the same rate and hitting the ground simultaneously.
If one or both objects are noticeably affected by air resistance, another factor comes into play, and the rule does not hold. For example, dropping a golf ball and a feather will result in the golf ball hitting the ground before the feather, which is greatly affected by air resistance and air currents.
Note that any object you drop is somewhat affected by air resistance. However, some are barely affected, such that the rule still holds.
Experimental verification
The fact that the acceleration due to gravity is independent of the mass of the objects has been verified many times.
In the 1600s, Galileo Galilei was said to have dropped two balls of different mass from the Leaning Tower of Pisa to prove that objects of different mass fall at the same rate. Some historians doubt whether he actually did the experiment at Pisa, but the experimental results are documented.
You can verify this experiment yourself by standing on a chair and dropping two balls or objects of different weights at exactly the same time. This is a rough experiment, but it can demonstrate the principle.
Summary
All objects will fall to the ground at the same rate, no matter what their weight or mass, provided air resistance is a negligible factor.
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Resources
The following resources provide information on this subject:
Websites
Acceleration due to Gravity Calculations - from Western Washington University
Gravitation and Gravity Resources
Books
Top-rated
books on Simple Gravity Science
Top-rated
books on Advanced Gravity Physics
Mini-quiz to check your understanding
If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.
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Effect of Mass on Acceleration Due to Gravity