How to Solve for Mass Using the Kinetic Energy Formula
All objects on earth, the sun, the moon, and even you are made of matter, and all matter has mass. In physics, mass is defined as, "A property of matter equal to the measure of an object's resistance to changes in either the speed or direction of its motion." In everyday language, mass is the "amount of stuff" that comprises an object. A larger object does not necessarily mean it has more mass. A ping-pong ball and a golf ball are about the same size, yet if both objects are dropped and land on your head from a second-story window, you would experience a major difference in the impact due to mass. Mass, then, is more easily understood by examining its role in the energy produced by matter that is in motion.
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Understanding Mass in the Kinetic Energy Formula
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Remember that matter in motion produces force, or energy. Recognize that when you push open a door with a single hand, your hand is exerting a force expressed by the formula: K = ½ MV2 , where:
- K is the amount of energy, normally expressed in scientific notation as joules
- M is the mass of the object in motion, normally expressed in kilograms
- V is the velocity of the mass in motion, normally expressed in meters per secondObserve that the force produced on the left side of the equation is the result of the products on the right side of the equation. Note: as the mass increases, then, the amount of the resultant energy/force also increases. To demonstrate this fact, use both hands to push open a door. Your increased mass with both hands results in greater force on the door, making the action easier.
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Kinetic Energy, Mass and Velocity
Clarify your understanding of mass by noting: for any given moving object, velocity alone is responsible for any increase or decrease in the force produced. For example, have a friend slowly roll a golf ball across the floor until it strikes your foot and feel the force of the impact. Next, have your friend throw the golf ball as hard as he can at your foot and feel the increased velocity that dramatically increases the resultant force against your foot. An increase in the velocity of any mass, therefore, increases its kinetic energy.
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How To Distinguish Between Weight and Mass
Remember that an object's mass and its weight are not the same. While it is a common practice to determine an object's mass by weighting it on a standard scale, note that this type of measurement is only accurate on the Earth's surface. On the Earth's surface, a one kilogram mass weighs about 2.2 pounds. But on Mars, the same kilogram mass would weigh only about 0.8 pounds. The mass would not change, but the weight would change because of the difference between the gravitational fields acting on the one kilogram mass.
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