Energy

Conversion of Energy

Forms of Energy

Energy

Work

Work• The product of force and distance

moved in the direction of the force• W = F x d• Units: Newton-meter, Nm

– Equivalent to Joule, J

Work Example

• A force of 10N is applied to a box to move it 2m along the floor. What is the work done on the box?

• A bodybuilder, 1.6 m tall lifted a 30-kg mass from the ground up to his head. How much work did he do?

Which force does more work?

Energy• The ability to do work• Work ~ Energy• Units: Nm, J• May be:

– Transferred– Stored– Transformed

Forms of Energy• Kinetic Energy

– Energy due to motion– Equation:

• EK = ½ mv2

• Potential Energy– Energy due to position– Equation:

• EP = mgh

Examples• What is the kinetic energy

of a 3-kilogram ball that is rolling at 2 meters per second?

• What is the potential energy of a 3 kilogram-ball that is 3m above the ground?

Forms of Energy• Chemical Energy

– Energy due to chemical reaction

• Nuclear Energy– Energy due to nuclear

reaction

Forms of Energy• Thermal Energy

– Energy transferred due to difference in temperature

• Electrical Energy– Energy due to

movement of charges

Forms of Energy

• Light Energy

• Sound Energy

Conversion of Energy

Conversion of Energy

Is this right or wrong?

Conversion of Energy

Example 1

• A box of mass of mass 3 kg is dropped from a height of 5m. Neglecting air resistance, calculate:– The potential energy of the box before it is

dropped– The kinetic energy of the box just before it

reaches the ground– The speed of the box just before it strikes the

ground

Example 2

• A ball of mass 60 g is thrown upwards with an initial speed of 30 m/s. If air resistance is negligible, calculate:– The initial kinetic energy of the ball– The initial potential energy of the ball– The potential energy of the ball when it reaches

its greatest height– The greatest height reached by the ball