What’s energy?

Anatoly · 2018-03-26 07:07:26

Seriously I just understood that I don’t get anything. What’s the definition for energy? There are so many forms of them. I’m confused. What is energy? And what’s the difference between the force F and energy E? The Newton formula F=mg tells us that if we know the position, mass and the force of every object on a plane, then we know everything about this space. What’s with energy now?

Luka504 · 2018-03-26 08:30:37

While energy and force do sound similar they are radically different.
Energy is something that is required for an object to do... anything. You need energy to do work.
Force is the interaction of 2 different objects, and if the force is strong enough, will move the object(s).
Just by the definition alone you can see how different they are.
In order to have any sort of Force, you need Energy to be able to do it.

TaskManager · 2018-03-26 09:09:45

alright
TO BEGIN WITH
ENERGY = MASS
exactly.
as Einstein's formula states, E = m * c^2. in this case, m is the mass of a body, E is the FULL energy of that body and c is the speed of light and in this case a conversion constant/coefficient.
if humanity had some kind of technology to turn matter (mass) into pure energy, that would be an outstanding breakthrough in development of engines and weaponry. this concept would be thousands of times more efficient than nuclear or even thermonuclear power. nuclear reactions provide lots of energy in a similar way, but they, simply put, convert only a tiny fraction of body's mass to energy. (it's actually much more complicated than that. if i recall correctly, this tiny fraction of body mass that is converted to pure energy is called "mass defect", you can take a more detailed read on it here)

Energy is a much more widely used term than force, you need energy to heat objects, you get energy back when you cool objects down, you have energy in nuclear physics, in optics, objects have kinetic energy when they are moving and potential energy when they are lifted above the ground, and so on and so forth

Force has little to do with energy directly and is a much simpler thing to understand
Newton's law: F = m * a
Where m is mass of a body, a is acceleration (speed of changing speed basically, measured in m/s^2) and F is the amount of force needed to apply to the body to give it such acceleration (or vice versa, a is the amount of acceleration body gets when pushed by force F)
The "F = mg" that you have mentioned in the OP is a specific case when we calculate the force that pushes body downwards, caused by gravity, this force is also called Weight (never confuse weight and mass!). in this case, a is replaced by g, which is Earth's gravitational constant (constant downwards acceleration) and equals approximately 9.81 m/s^2. this value is different for other planets.
in general, force is just that thing that pushes objects around. how much does it push them? that depends on the mass of these objects. thats pretty much it

tl;dr: energy is our everything, force is used solely for pushing/throwing/moving stuff around
(i also realised that i went slightly offtopic on some points sry)

Luka504

Emma333 · 2018-03-26 10:21:12

In school terms:

Force is measured in Newton (N)
Energy is measured in Joule (J) , aka Newton meter (N m)
Kinetic energy is the energy an object has that makes it move
Potential energy is the energy that's created by gravity
To get kinetic energy out of force you need work, which is measured in Newton meter too.

If an object is moving it has kinetic energy. So if you're pushing an object, you're giving it kinetic energy by using force. This transition is called Work, the formula that's used is: W = F*s. Work is the amount of kinetic energy that's giving to an object by using force. So to get the difference in kinetic energy, you use the formula: W(totale) = Delta E(kinetic). The totale amount of kinetic energy is the kinetic energy you had before plus the total amount work.
Another way to get the total amount of kinetic energy is by using the formula: E(kinetic) = 1/2 * m * v^2, where m is mass, and v is velocity. In this formula you can see that the kinetic energy is zero when the velocity is also zero.

Unlike Force, energy is constant. When energy gets lost in one aspect, it enters another aspect. So when kinetic energy is created, another form of energy will become less. The most common scenario in schoolbooks is that the potential energy becomes less when the kinetic energy becomes more. Potential energy on earth: E(potential) = m * g * h, where m is mass, g is the gravitational constant on earth (9,8 in Germany) and h is height.
Imagine a ball being thrown in the air. By throwing it you're giving kinetic energy to the ball, you can measure the amount of kinetic energy by using: E(kinetic) = 1/2 * m * v^2. When you're throwing it, the height of the ball is still low, so the potential energy is low too. When the ball gets higher and higher, the velocity becomes less until the ball stops moving for a moment. This means that E(kinetic) gets lower the higher the ball is, and E(potential) gets higher the higher the ball is. You can see that the total of these energies should be constant.

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#1 2018-03-26 07:07:26

What’s energy?

#2 2018-03-26 08:30:37

Re: What’s energy?

#3 2018-03-26 09:09:45

Re: What’s energy?

#4 2018-03-26 10:21:12

Re: What’s energy?

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