Kinetic energy?
Do we normally measure kinetic energy directly? If so explain, if not, how do we normally get it, and could we measure kinetic energy directly?
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answers:
electron1 say: The following equation is used to calculate an object’s kinetic energy.
KE = ½ * mass * (velocity)^2
We need to know the mass and velocity of the object. Let’s assume a 1000 pound car has a velocity of 60 mph. One pound is 0.454 kilograms.
Mass = 1000 * 0.454 = 454 kg
1 mph * 5280 ft/mi * 12 in/ft * 2.54 cm/in * 1 m/100 cm * 1 hr/3600 s = 0.44704 m/s
v = 60 * 0.44704 = 26.8224 m/s
KE = ½ * 454 * 26.8224^2
This is approximately 1.633 * 10^5 J. I hope this answers your question.
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Morningfox say: I don't know what you mean by "directly". When you get down to extreme basics, we measure everything by differences in time and position. At time T1, this thing was at position X1. At time T2, the same thing was as position X2. Some people could argue about how we know that it's the same thing each time. Other people could argue about how we "know" anything at all, including times and positions.
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busterwasmycat say: Kinetic energy of what? We tend to employ temperature as a proxy for average mean kinetic energy at the atom scale. With larger objects, we can calculate bulk kinetic energy based on motion and definition of mass, and we can get mass from the change in motion under force (like gravity), so we measure things that allow us to know kinetic energy. Otherwise, to measure kinetic energy, you basically have to interact with the object and change its kinetic energy. That is, fundamentally, how we came up with the recognition of how to define kinetic energy in terms of mass and velocity. I don't now have to go out and smash cars against a spring-loaded wall (or whatever) to define the kinetic energy of that object at different velocities (speeds).
The only true measurement of kinetic energy would require stopping the object and seeing how much energy gets released (kinetic energy is zero at zero velocity and the energy must go somewhere). That isn't very practical.
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