Science >> Physics for Kids What is kinetic energy? Kinetic energy is the energy an object has due to its motion. As long as an object is moving at the same velocity, it will maintain the same kinetic energy. The kinetic energy of an object is calculated from the velocity and the mass of the object. As you can see from the equation below, the velocity is squared and can have a significant impact on the kinetic energy. Here is the equation for calculating kinetic energy (KE):
KE = 1/2 * m * v2
where m = mass and v = velocity
How to Measure Kinetic Energy
The standard unit for kinetic energy is the joule (J). The joule is the standard unit for energy in general. Other units for energy include the newton-meter (Nm) and the kilogram meter squared over seconds squared (kg m2/s2).
Kinetic energy is a scalar quantity, which means it only has a magnitude and not a direction. It is not a vector.How is it different from potential energy?
Kinetic energy is due to an object's motion while potential energy is due to an object's position or state. When you calculate an object's kinetic energy, its velocity is an important factor. Velocity, however, has nothing to do with an object's potential energy.energy due to its velocity.
Example Using A Roller Coaster One way to think of potential and kinetic energy is to picture a car on a roller coaster. As the car travels up the coaster it is gaining potential energy. It has the most potential energy at the top of the coaster. As the car travels down the coaster, it gains speed and kinetic energy. At the same time it is gaining kinetic energy, it is losing potential energy. At the bottom of the coaster the car has the most speed and the most kinetic energy, but also the least potential energy. Example problems: 1. A car and a bicycle are traveling at the same speed, which has the most kinetic energy? The car does because it has more mass. 2. A ball weighs around 1 kg and is traveling at 20 meters per second, what is its kinetic energy?
KE = 1/2 * m * v2
KE = 1/2 * 1kg * (20 m /s)2 KE = 200 J 3. A boy weighs 50 kg and is running 3 meters per second, what is his kinetic energy?
KE = 1/2 * m * v2
KE = 1/2 * 50 kg * (3 m/s)2 KE = 225 J
Interesting Facts about Kinetic Energy
- If you double the mass of an object, you double the kinetic energy.
- If you double the speed of an object, the kinetic energy increases by four times.
- The word "kinetic" comes from the Greek word "kinesis" which means motion.
- Kinetic energy can be passed from one object to another in the form of a collision.
- The term "kinetic energy" was first coined by mathematician and physicist Lord Kelvin.
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Science >> Physics for Kids
Zeldredge's answer is great, answering the question from a mathematical point of view. Since you asked this question in a physics forum, I'll just add to that by answering from a physical point of view, clarifying why the energy is linear in mass and not quadratic:
Suppose you have two objects of equal mass moving parallel to each other with velocity $v$, each of mass $m$, and thus each of energy $\frac{1}{2}mv^2$. Although the two objects don't have anything to do with each other, we can calculate the sum of their energies if we want, and get $mv^2$.
Now attach the masses by a thin thread with negligible mass. This doesn't change the energy of any of the masses, and neither does it change their sum. Regarding now the masses as one single object of mass $2m$, the energy of this object must be $\frac{1}{2}\times(2m)\times v^2 = mv^2$, which is equal to the sum we calculated before.
That is, if an object has twice the mass, it also has twice the energy. If it had four times the energy, that would mean that by attaching two objects by a thin thread, you could increase the total energy, which would mean violating the law of energy conservation — one of the worst offenses you can commit.
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