Chapter 11 Flashcards
Kinetic Energy
the energy an object has due to its motion
What is the amount of kinetic energy an object has depend on?
mass and speed
The formula for kinetic energy
Ek = 1/2 mv^2
What is the “Work Energy Theorem?”
The work done to the object quals its change in kinetic energy, or in symbols, W = ΔEk
Units for kinetic energy:
Joules
When is the work done to an object negative?
When force is opposite to motion because energy has decreased and causes a negative change in Ek
Potential energy
The energy stored in an object due to its position, shape or form
Examples of potential energy:
e.g. - the gravitational potential energy of a rock lifted up - chemical energy in food or fuels - nuclear energy stored in the nucleus of the atom - electrical energy in wires - elastic energy in a kicked ball, pole vaulter’s pole, spring, tennis racket, etc.
What is mass according to Einstein
According to Einstein, mass itself is a form of potential energy -
How does a pole vaulter illustrate how energy is converted from one form to another?
- chemical energy from food → kinetic energy of person → elastic potential energy of bent pole → some kinetic and then gravitational potential energy of person → kinetic energy as a person falls → sound and heat when a person lands
when we talk about potential energy, what are we really talking about?
Gravitational potential energy, since in this chapter, we are only dealing with potential energy due to an object’s position,
Forumla for potential energy:
Ep/Eg = mgh
This only applies near the earth’s surface where we can use the value “g”
Units for potential energy
joules
Why does W = ΔEp
Just like with kinetic energy, an object can have some potential energy to start with, so really the work done to an object is equal to its change in potential energy.
At what position does an object have zero potential energy?
eg. a book held one meter above the desk - Should its height be measured from the desktop?, the floor?, or the ground outside the window? or sea level? * It really doesn’t matter.
What is all that matters with potential energy?
While we can quite easily say how much kinetic energy an object has, we can only say how much potential energy an object has relative to whatever reference point you choose. All that really matters is the change in potential energy from one point to another.
Law of conservation of energy
Within a close, isolated system, the total amount of energy is constant. It cannot be created or destroyed. It can only be transferred from one object to another or changed from one form to another.
Since energy is a scalar, how is it conserved in an explosion? (there is no kinetic energy before the explosion and lots of kinetic energy after)
it is converted from chemical potential energy to kinetic energy.
What is mechanical energy?
Gravitational potential energy and kinetic energy together.
What equation do you use when speeds approaching the speed of light are involved?
Ek = 1/2mv^2 does not hold true. Instead, we must use equations from Einstein’s Theory of Relativity.
