Gravity and Free Fall. Gravity. Sir Isaac Newton (1642-1727) developed a law of gravitation which said all objects in the universe attract each other through gravitational force Universal Gravitation Equation F = G m1m2 d 2
Free fall- when gravity is the only force acting on an object (free fall acceleration is directed toward center of earth)
The acceleration of gravity (g) for objects in free fall at the earth's surface is 9.8 m/s2.
Galileofound that all things fall at the same rate in the absence of air resistance, regardless of their mass
The rate of falling increases by 9.8 m/s every second.
Height = ½ gt2
½ (9.8 )12 = 4.9 m½(9.8)22 = 19.6 m
½ (9.8)32 = 44.1 m
½ (9.8)42 = 78.4 m
Mass and Weight different!
► Mass is an intrinsic property of an object. It is completely determined by the number and type of atoms that make up the object. It does not depend on the environment in which the object is located.
► But weight is different. Weight depends on both the object itself, and on some other object that exerts the gravitational force.
So, for example, the mass of an object would be the same on the moon or the Earth; but the weight would be different.
Weight = the force of gravity
The weight of an object is, by definition, the strength of the force of gravity pulling the objectdownward.
W = m g
W = mg
If released, the acceleration of m would be …
By Newton’s second law the force on m must be …
What is the force acting on the mass m due to the Earth’s gravity?
g = 9.81 m/s2
That is, the magnitude, or strength, is mg and the direction is downward.
By the way, what is the reaction force?
A ball thrown horizontally will fall at the same rate as a ball dropped directly.
A ball thrown into the air will slow down, stop, and then begin to fall with the acceleration due to gravity. When it passes the thrower, it will be traveling at the same rate at which it was thrown.
Example. Playing catch with a softball
The trajectory has 3 parts.
What is the force acting on the ball, during each part of the trajectory?