Kinetic energy and potential energy of a baseball

In summary, the kinetic energy of a baseball cannot be negative, but the potential energy can be negative when the ball is falling. The equations for kinetic and potential energy are KE=1/2mv^2 and PE=mgh respectively. These energies can be thought of as bank accounts, with kinetic energy being the speed of the ball and potential energy being the height or distance from a reference point. The kinetic energy can never be negative, but the potential energy can if the reference point is below the ball's position.
  • #1
physicsman2
139
0

Homework Statement



can the kinetic energy of a baseball be negative.
can the potential energy of a baseball be negative.

Homework Equations


no relevant equations.


The Attempt at a Solution


i believe the potential energy can be negative if it is falling and the kinetic energy can be negative if the ball is hit with a greater force over a longer distance than it was thrown in the opposite direction
Am i right?
 
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  • #2
What is the equation for kinetic energy?

What is the equation for potential energy?

Remember that when using potential energy we can use ANY reference level, (i.e. we can choose the ground to be h=0, or halfway up into the atmosphere to be h=0). We are not able to give an exact value of the potential energy, we can only ask : "What is the potential energy change of this particle with respect to this point?" ie the potential energy of a baseball that is about to be dropped on your head from 6' is a lot smaller and will hurt a lot less if you are standing up at 5'5" just under the ball then laying down! :-)
 
  • #3
sorry i worded the questions wrong:

Can the kinetic energy of a baseball ever be negative.
Can the gravitational potential energy of a baseball ever be negative.

PE=mgh.
KE=1/2mv^2
 
  • #4
So, what are the possible values for those two equations, given that m is always possitive, g is possitive. The kinetic energy of an object is a measure of the work that would be done if it was brought to a stop, i.e. if I throw a baseball at a watermelon it will crack open.

I think the negative kinetic energy example you gave above was saying that if you throw a baseball at me, and then I hit it with my bat and send it flying in the other direction then the kinetic energy is now negative, but if the ball comes back and hits you it will hurt! This means it had energy! If there is any energy form that has negative energy, it would mean it has a LACK of energy, i.e. it would take work to give it any energy at all.

Kinetic and potential energy can be thought of as bank accounts, raising a ball is synonymous to putting money in the bank (potential energy) that you can use later to buy stuff (do work!)

For kinetic energy, you can think of the speed of the ball as the bank account balance, the higher the speed, the higher the kinetic energy. If you stop it, all the kinetic energy is used up.
 
  • #5
thank you very much it all makes sense now
 
  • #6
You are very welcome, what answers did you get? I just want to make sure! :D
 
  • #7
the kinetic energy can't be negative while the gravitational potential energy can be negative
 
  • #8
That's right ;).
 

1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. In the case of a baseball, it is the energy it has while it is in motion, such as when it is being thrown or hit.

2. How is kinetic energy calculated for a baseball?

The formula for calculating kinetic energy is KE = 1/2 * m * v^2, where m is the mass of the object and v is the velocity or speed of the object. For a baseball, the mass is typically around 0.145 kilograms and the velocity can vary depending on the pitch or hit.

3. What is potential energy?

Potential energy is the energy an object possesses due to its position or state. In the case of a baseball, it is the energy it has while it is at rest, such as when it is sitting on the ground or on a pitcher's hand.

4. How is potential energy calculated for a baseball?

The formula for calculating potential energy is PE = m * g * h, where m is the mass of the object, g is the acceleration due to gravity (9.8 m/s^2), and h is the height of the object from a reference point. For a baseball, the mass and acceleration due to gravity are constant, but the height can vary depending on its position.

5. How are kinetic and potential energy related for a baseball?

Kinetic and potential energy are both forms of energy that a baseball can possess. When a baseball is in motion, it has kinetic energy, but when it is at rest, it has potential energy. The two energies are interconvertible, meaning that when a baseball is thrown or hit, its potential energy is converted into kinetic energy, and vice versa when it comes to a stop. Ultimately, the total energy (kinetic + potential) of a baseball remains constant, in accordance with the law of conservation of energy.

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