I.P.C. 6 A

Describe the law of conservation of energy. (This law includes

calculation of G.P.E.)

Conservation of Energy

Energy in a system may take on various forms (e.g. kinetic, potential, heat, light). The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant.

Example: A roller coaster on top of a hill has potential energy. When the roller coaster rolls downward the PE is converted into Kinetic Energy.

• The sun or solar energy is the source of energy for all living organisms.

• In photosynthesis, plants convert solar energy into stored glucose (sugar) energy.

• This energy is transferred to animals through the food chain

APPLYING THE CONSERVATION OF ENERGY

Electrical Energy

Heat Energy

Mechanical Energy

(Energy can be converted from one form of energy to another, but energy never just appears or disappears.)

Which of the following is an example of solar energy being converted into chemical energy?

A. Plants producing sugar during the day

B. Water evaporating and condensing in the water cycle

C. The sun unevenly heating Earth’s surface

D. Lava erupting from volcanoes for many days

Answer: A, because plants use sunlight to make sugar which is a stored chemical energy for them to use.

TAKS 2004

Why is the sum of the products’ energy in this reaction less than the sum of the reactant’s energy?

A. Energy is given off as heat

B. The products absorb available energy

C. Energy is trapped in the reactants

D. The reactants’ energy is less than the melting point of glucose

Answer: A, because energy is not lost or gained but can be converted to other forms. Heat or Thermal Energy is one common conversion.

TAKS 2004

An inventor claims to have created an internal combustion that converts 100kJ of chemical energy from diesal fuel into 140kJ of mechanical energy. This claim violates the law of conservation of:

A. momentum

B. inertia

C. energy

D. mass

Answer: C, because by changing 100kJ of energy into 140kJ you have created energy which violates the law of conservation of energy.

TAKS 2004

Fuel cells powered by plankton from the seabed can be used to operate instruments that monitor ocean currents and water temperature. These fuel cells get their energy by converting –

A. chemical energy to electrical energy

B. electrical energy to mechanical energy

C. hydroelectric energy to geothermal energy

D. mechanical energy to chemical energy

Answer: A, because plankton (plants) convert sunlight to glucose (chemical energy) which is converted to electrical energy to power fuel cells.

YOUR TURN

GET OUT GET OUT SCRAP PAPER SCRAP PAPER

AND YOUR AND YOUR FORMULA FORMULA

CHARTCHART

Formula Chart

Constants, Symbols and

Units

Formulas

K.E. andK.E. andG.P.E.G.P.E.

Today we will work with the kinetic

energy and gravitational

potential energy formulas. Find them

on your Formula Chart.

KINETIC ENERGY

Kinetic energy is the energy of motion. An object which has motion - whether it be

vertical or horizontal motion - has kinetic energy. There are many forms of kinetic energy - vibrational (the energy due to

vibrational motion), rotational (the energy due to rotational motion), and translational

(the energy due to motion from one location to another).

What is the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s.

Answer: D 1.05 x 105 Joules

K.E. = (625) x (18.3)2

2= 104653.12 J

POTENTIAL ENERGYPotential energy is energy that is stored in an object. (A stretched rubber band has potential energy. When you release the stretch the

potential energy is converted to kinetic energy and the rubber band flies through the air. (Kinetic energy is

energy of motion) Notice the potential energy was changed to kinetic energy

but no energy was lost or gained. Gravitational potential energy is the energy stored in an object as the result

of its vertical position or height. (Example a boulder on top of a

mountain)

GRAVITY

Formula Chart

Gravity = 9.8 m/s2

Constants, Symbols and

Units

Formulas

In GPE problems we need to know what

force gravity exerts. Where do we get the

information?

What is the potential energy of the rock?

A. 59,900 J

B. 64,600 J

C. 93,100 J

D. 121,500 J

TAKS 2003

What is the potential energy of the rock?

A. 59,900 J

B. 64,600 J

C. 93,100 J

D. 121,500 J

TAKS 2003

P.E. = (95)(9.8)(100)

What is the approximate difference in gravitational potential energy of the two shaded boxes?

A. 19 J

B. 39 J

C. 59 J

D. 79 J

TAKS 2005-06

What is the approximate difference in gravitational potential energy of the two shaded boxes?A. 19 J

B. 39 J

C. 59 J

D. 79 J

TAKS 2005-06

58.8 – 19.6 = 39.2 J

P.E. = (2)(9.8)(3.0) =58.8

P.E. = (2)(9.8)(1.0) =19.6

FOLDABLE TIME

Make a Foldable for Gravitational Potential Energy and Kinetic

Energy