Download Kinetic Energy is Energy Due to Motion When the potential energy of

Kinetic Energy is Energy Due to Motion
When the potential energy of an object is released, that object
often begins to move. Moving objects can do work. A falling
hammer can drive a nail into wood. Moving molecules in hot
steam can turn turbines. Moving molecules in a sound wave can
make your eardrum vibrate.
Any moving object has kinetic energy. When a solid object
moves, all the molecules move in unison. The kinetic energy of
such an object is often called mechanical kinetic energy. Even
when molecules are not physically attached to each other, they can
still move together like air molecules in the wind.
Thermal energy is the kinetic energy of individual molecules
moving in a random manner.
The kinetic energy of a moving object is determined by the
mass and speed of the object. The relationship between kinetic
energy, mass and speed is represented by the following equation
Ek = ½ mv2
Where:
Ek is the energy of the object (in Joules)
m is the mass of the object (in kilograms)
v is the velocity of the object (in meters per second).
This formula will still produce the proper units for energy
(recall that a joule is actually a kgm2/s2).
A Look at Kinetic Energy & Potential Energy in the Three
States of Matter
Solid:
Low Kinetic Energy – slow moving
Low Potential Energy – Particles close
together
Liquid:
Higher Kinetic Energy – moving faster
Higher Potential Energy – Particles are
further apart
Gas:
Very High Kinetic Energy – moving very
fast
Very High Potential Energy – particles are
very far apart
]
Important Concept: When heat (a form of energy) is added to a
substance the energy will EITHER speed up the particles
(increase Ek) OR increase the distance between them (increase Ep),
but NOT BOTH AT THE SAME TIME.
Questions:
1. Which has more kinetic energy, a semi truck travelling
30km/hr or a bicycle travelling 30km/hr? Why?
2. Water does not always freeze at 0C it can be cooled to –20
or 30C if conditions are right. Which has more total thermal
energy, liquid water at -10C or ice at the same temperature?
Why?
3. You are heating a substance but its temperature is not
increasing what type of energy is being increased? Why?
4. You are cooling hot iron in cold water, what kind of energy is
being lost by the iron? Why?
5. The water in the above question evaporates when the iron
touches it, what type of energy is being increased in the
water? Why?
6. You apply a force of 1000N to a baseball, and it travels a
distance of 80m. You apply this same force to a rail car and
it does not move at all, have you done work in both cases?
Why or why not?