What's the difference between energy and force?

[kashiark]

Is force just acting energy?

 

[Nabeshin]

Well for one they're completely different.

For two one is a vector the other is a scalar.

 

[kashiark]

How are they completely different?

 

[Bob S]

For one thing, if the energy E is stored energy due to a force F_x in the direction x, then the force is given by the derivative

F_x= dE/dx

For example, if the stored energy E of a mass m is mgy, then the force is

F_y = d(mgy)/dy = mg.

Bob S

 

[kashiark]

So force is just the rate of change of energy?

 

[A.T.]

So force is just the rate of change of energy?

No, that's power. Force is the rate of change of momentum.

 

[Nabeshin]

So force is just the rate of change of energy?

No, that's power. Force is the rate of change of momentum.

Note that "rate of change" by itself doesn't mean anything. You have to specify rate of change with respect to what, which is where the distinction arises:
$$F=\frac{dp}{dt}$$

$$F=\frac{dE}{dx}$$

$$P=\frac{dE}{dt}$$

 

[A.T.]

Note that "rate of change" by itself doesn't mean anything.

True. I assumed with respect to time.

 

[Bob_for_short]

Is force just acting energy?

Yes, exactly.

If we speak of potential energy U(r) the force F is -dU/dr. dr is the vector indicating in what direction the energy is acting.

If we speak of kinetic energy in collision T=mv²/2, the force result (work) is ∆T.

Together they can give you the complete solution of a problem.

 

[kashiark]

Ok, I think that I've got it: Force is rate of change of energy with respect to a particular dimension, and it's the rate of change of momentum with respect to time. What is energy measured in? Kg*m²/s²?

 

[mikelepore]

I think this is more like plain English:

A force is a push or a pull applied to something. A force has the ability to overcome the inertia of an object (its tendency to keep the same velocity) and cause it to accelerate (change its velocity). The mass of the object is the constant of proportionality between the force and the resulting acceleration (F=ma). If the force is able to displace an object, the force does work on it, but, if the force is exactly balanced by another force that has the opposite direction, the net force will be zero, and no work will be done on the object. The net work done on an object equals the change in its kinetic energy.

 

[mikelepore]

What is energy measured in? Kg*m²/s²?

The equations show that work and energy have the same units:

unit of acceleration
m/s^2

force = (mass)(acceleration)
1 Newton = 1 (kg)(m/s^2) = 1 kg m/s^2

work = (force)(displacement)
1 joule = 1 (kg m/s^2)(m) = 1 kg m^2/s^2

... or ...

kinetic energy = (1/2) m v^2
1 joule = 1 (kg)(m/s)^2 = 1 kg m^2/s^2