All you need to know about gravity
Gravitation Building on the work of Galileo and Kepler, Isaac Newton formulated the theory of gravitation in the 1680s. The story goes that Newton was sitting under a tree when an apple fell and hit him on the head. This made him curious and inspired him to determine that there was a force called gravity that pulled the apple down from the tree.
Universal Gravitation This force on Earth pulls everything toward the ground. Newton determined that all masses of matter attract each other through the force of gravity. This is called the Theory of Universal Gravitation. What this means is that not only does the Earth pull the apple toward it by the force of gravity, but the apple also pulls the Earth toward it by that same force.
(See Newton's Universal Gravity Equation for more information.)
Modern theories It wasn't until the early 1900s that Albert Einstein gave another interpretation of the force gravity in his General Theory of Relativity. He stated that gravitation was the result of the curvature of space around matter and not due to some force. Recently there have been new theories that the force of gravity is caused by graviton particles or by waves. Those theories satisfy rules of Quantum Mechanics that Einstein's concepts d
idn't.
(See Modern Views of the Force of Gravity for more information. )
Gravity on Earth The force of gravity from the mass of the Earth pulls your mass toward the ground and prevents you from floating off into space. Of course, your mass pulls the Earth and contributes to the total force.
The equation for the force of gravity for all objects relatively close to the Earth is:
F = mg
where
Note: g is often called the acceleration of gravity. That is incorrect and misleading, since gravity does not accelerate. The expression should be the acceleration due to the force of gravity, which is a more accurate definition for g.
Weight The weight of an object is the measurement of the force of gravity on that object. You weigh something on a scale, according to the force that the Earth pulls it down. Thus the weight is actually the force of gravity on that object:
Universal Gravitation This force on Earth pulls everything toward the ground. Newton determined that all masses of matter attract each other through the force of gravity. This is called the Theory of Universal Gravitation. What this means is that not only does the Earth pull the apple toward it by the force of gravity, but the apple also pulls the Earth toward it by that same force.
(See Newton's Universal Gravity Equation for more information.)
Modern theories It wasn't until the early 1900s that Albert Einstein gave another interpretation of the force gravity in his General Theory of Relativity. He stated that gravitation was the result of the curvature of space around matter and not due to some force. Recently there have been new theories that the force of gravity is caused by graviton particles or by waves. Those theories satisfy rules of Quantum Mechanics that Einstein's concepts d
(See Modern Views of the Force of Gravity for more information. )
Gravity on Earth The force of gravity from the mass of the Earth pulls your mass toward the ground and prevents you from floating off into space. Of course, your mass pulls the Earth and contributes to the total force.
The equation for the force of gravity for all objects relatively close to the Earth is:
F = mg
where
- F is the force pulling objects toward the Earth; it is also the weight of the object
- m is the mass of the object
- g is the acceleration due to gravity; this number is a constant for all masses of matter
- mg is the product of m times g
Note: g is often called the acceleration of gravity. That is incorrect and misleading, since gravity does not accelerate. The expression should be the acceleration due to the force of gravity, which is a more accurate definition for g.
Weight The weight of an object is the measurement of the force of gravity on that object. You weigh something on a scale, according to the force that the Earth pulls it down. Thus the weight is actually the force of gravity on that object:
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