Section 1 The Nature of Energy Energy is

Section 1: The Nature of Energy • Energy is the ability to cause change. • There are many different forms of energy: – chemical – thermal – kinetic – potential – electrical

Potential and Kinetic Energy

Kinetic Energy • energy in the form of motion • KE = ½ mass x velocity 2 KE = ½ m x v 2 • SI unit—Joule (J)

Potential Energy • stored energy due to position • types of potential energy – elastic: energy stored by something that can stretch or compress (ex. rubber band, spring) – chemical: energy stored in chemical bonds (ex. gasoline, food) – gravitational: energy stored by objects that are above Earth’s surface (ex. apple or leaf in tree)

Gravitational Potential Energy (GPE) • GPE = mass x 9. 8 m/s 2 x height • SI unit—Joule (J) • Bjorn is holding a tennis ball outside a 2 nd story window (3. 5 m from the ground) and Billie Jean is holding one outside a 3 rd story window (6. 25 m from the ground). How much more GPE does Billie Jean’s tennis ball have? (Each tennis ball has a mass of 0. 06 kg).

Section 2: Conservation of Energy • Energy is most noticeable as it transforms from one form to another. • mechanical energy = total energy (kinetic + potential) Bonus: How do your kinetic and potential energy relative to an elevator change as you go up?

Energy Conversion

Law of Conservation of Energy • Energy cannot be created or destroyed. • The total amount of energy in the universe remains constant.

Work (Chapter 5 -1) • Work is the transfer of energy that occurs when a force makes an object move. • Two conditions must be met for work to be done on an object: – the object has to move – the movement must be in the direction of the force

Work and Energy • When work is done, a transfer of energy always occurs.

Calculating Work • Work = force x distance W=Fxd • SI unit: Joules (J) • One joule is about the amount of work required to lift a baseball a vertical distance of 0. 7 m.

Example Problems • You move a 75 kg refrigerator 35 m. This requires a force of 90 N. How much work was done while moving the refrigerator? – 3150 J • When you and a friend move a 45 kg couch to another room, you exert a force of 75 N over 5 m. How much work did you do? – 375 J

Bonus • Suppose you used a force of 50 N to shoot an arrow, and the arrow flew 25 meters. As you shot the arrow, the bow string moved the arrow 1 m. Did you do 1250 J of work or 50 J of work? Explain. – You did 50 J of work, because after the arrow left the bow, it was flying loose in the air and was not experiencing any force from you.

Power • Power is the amount of work done in a certain amount of time (the rate at which work is done). • Power = work / time P=W/t • SI unit: watts • Example: How much power is required to push a car for 10 s if the amount of work done during that time is 5, 500 J? – 550 W

Temperature and Heat (Chapter 6) • All matter is made up of tiny particles in constant motion, meaning that they have kinetic energy. • temperature: average kinetic energy of the particles

• thermal energy: total energy of all the molecules in an object • A larger mass has more thermal energy than a smaller mass at the same temperature, because there are more particles in the larger mass. • When the temperature of an object increases, the average kinetic energy of the molecules increase, so thermal energy increases.

Heat • heat: energy that is transferred from an object at a high temperature to one at a lower temperature • Heat and work are similar. Both are energy being transferred. Both are measured in joules. • calorimeter: instrument used to measure changes in thermal energy

Transferring Thermal Energy

Conduction • conduction: transfer of energy through matter by the direct contact of particles • Conduction occurs because of the collisions between particles. • insulators: material that doesn’t allow heat to flow through it easily

Convection • fluid: anything that flows (liquids, gases) • convection: transfer of energy in a fluid by the movement of the heated particles • Convection currents are rising-and-sinking actions that transfer heat from warmer to cooler parts of a fluid.

Radiation • radiation: transfer of energy by electromagnetic waves • Electromagnetic waves can travel through space even when no matter is present. • When radiation strikes a material, some of the energy is absorbed, some is reflected and some may be transmitted through the material.