1. Energy and Momentum

2. Energy Energy is the work required to do something
Energy is a scalar quantity (it does not have a direction)
Energy can take many forms, ie light energy, sound energy, heat energy, mechanical energy, potential (stored) energy, chemical energy and nuclear energy
Energy transfers and transforms can be measured.
Transform example: chemical->electric->mechanical
The conservation of energy principle states that energy cannot be created or destroyed.

3. Transferring energy Listed below are different energy transfers:
Emission or absorption of EM or Nuclear radiation
Heating and cooling of an object or substance as result of temp difference.
The action of a force on an object resulting in movement
Student Task : In groups construct an energy transformation flow chart for the light energy of a florescent light tube in your class room.

4. Work and Kinetic Energy
Woirk !!!!
Work and Kinetic Energy
The mechanical energy required to move an object a certain distance is called work and is defined as:
Kinetic Energy (KE) is the energy required to make an object move.
So from the definition of work we can say that.....

5. Maynard G. Krebs will always be best remembered for his response whenever anyone mentioned the subject of work.  He would instantaneously shudder, and let out a plaintiff cry of "WORK!?!?"

6. Multiply both sides by m
Kinetic Energy -I
But, from Newton's Second law we know that
Substituting into I
We also know that
But initially
Multiply both sides by m

7. Kinetic Energy
Therefore, we can write work as:
Tadda!

8. Kinetic Energy Units
In the SI (metric) system of units: • m is expressed in kg (kilograms), • v is expressed in ms-1 (meters per second), • the energy is expressed in J (joules).

9. Note that if the velocity of an object is doubled, its kinetic energy is quadrupled.
Kinetic energy can also can be converted into other forms of energy.
For example on mountain roads runaway lanes are often provided for trucks that lose their brakes while going down long hills. The runaway lane takes the truck back uphill and allows the truck to coast to a stop as its kinetic energy is converted to potential energy.

10. Questions
1. A truck with mass 5000kg is moving at 10m/s. What is the initial kinetic energy of the truck?
2. Two cars of mass 1000kg traveling at 60km/hr collide head on
and lock together on impact (are stationary after impact).
i) what is the kinetic energy lost in the collision?
ii) where does it go?
3. A body of mass 50kg is traveling at 20m/s. It is then brought to rest by a constant force in a distance of 5m.
Calculate: i) loss in KE of the body ii) Work done by the body against the retarding force iii) the magnitude of the force

11. Transformation of Energy
Collisions: The energy lost in a collision is transformed into the following energies
Sound energy: some energy lost in the collision is transferred to the air molecules, causing them to vibrate rapidly thus producing the loud bang that we sometimes hear.
Thermal energy: Heat is produced as the result of rapid movement of particles within a substance. The KE of the object is transferred to the particles within it, thus causing heat.
Potential energy of deformation: potential energy stored in an object as a result of changing its shape. An example of this would be a spring.