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Drew777
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What would it mean when you subtract potential energy of a higher elevation from the summation of energy(kinetic + potential of a lower elevation)?
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Kinetic energy can't be negative. A constant sum for gravitational potential energy and kinetic energy only occurs if there are no other forces involved. If some force other than gravity affects an object, then the work done by that force also affects the total energy.Drew777 said:So is it possible to get a negative number as the kinetic energy of the higher elevation?
rcgldr said:Kinetic energy can't be negative. A constant sum for gravitational potential energy and kinetic energy only occurs if there are no other forces involved. If some force other than gravity affects an object, then the work done by that force also affects the total energy.
Drew777 said:I understand that. When I take the the potential energy of the higher point and subtract it from the kinetic energy I get a negative number. What does this mean?
willem2 said:kinetic energy can't be negative.
It means that a thrown object will fall back before it gets to this altitude.
If you throw something straight up, it will start to move down again when the kinetic energy is 0.
Drew777 said:What I have is the potential energy of a low point that I will call PEf and I got the kinetic energy it took for the object to move down the incline(KEf). I added them together to get Ef.
Now I have to take this number Ef and subtract it from the higher point of potential energy, that I will call PE. I ended up with a negative number on all my trials but one. Why would this be?
Drew777 said:The KEf I measured was using 1/2(m)(Vf^2). So the KEf is the kinetic energy from the high point (PEhp) to the lower point(PEf).
In the ideal (frictionless) case, since mechanical energy is conserved, ΔE should be 0 in all cases. (All potential energy lost during the descent is converted into kinetic energy). The fact that you get a negative ΔE means that mechanical energy is lost. This must be a combination of experimental error + the fact that the table is not entirely frictionless. It's probably mostly the latter, a consequence of which is that although total energy (as always) is conserved, mechanical energy (which means kinetic + potential) is not conserved. Some of the mechanical energy is converted into heat by friction. That's where the shortfall comes in: it's the work done by the frictional force.Drew777 said:To get Ef I added PEf + KEf.
Now I need to find Δ E. The equation for Δ E is Ef-PEhp.
Example
PEf + KEf=Ef
2,070,000 ergs + 623,000 ergs=2,690,000 ergs
Ef - PEhp=Δ E
2,690,000 ergs - 2,810,000 ergs= -107,000 ergs
All of my trials came out with a negative number except my last trial. It came out with a +20,000.
I am trying to understand where these numbers are coming from. Is -107,000 just the energy lost from the top to the bottom. If so then where did the positive number come from?
Thanks
Drew
Potential energy is the energy that an object has due to its position or state. It is stored energy that can be converted into other forms of energy, such as kinetic energy.
Kinetic energy is the energy an object possesses due to its motion. It is directly proportional to the mass of the object and the square of its velocity.
Potential energy and kinetic energy are two forms of energy that are interconvertible. When an object falls, its potential energy decreases and its kinetic energy increases. Conversely, when an object is lifted, its potential energy increases and its kinetic energy decreases.
Some examples of potential energy include a stretched rubber band, a compressed spring, and water at the top of a dam. These objects have the potential to do work or move due to their position or state.
Examples of kinetic energy include a moving car, a flying airplane, and a spinning top. These objects have energy due to their motion and can do work by transferring this energy to other objects.