ENERGYJuan Francisco García

Science9th Grade

WHAT IS ENERGY?In which way the transformations of energy influence the development of society?

ENERGY

Energy is the ability to do work.

• Work is done when a force causes an object to move in the direction of the force.

When one object does work on another, energy is transferred from the first object to the second object.• It is expressed in units of joules (J).

TYPES OF ENERGYMECHANICA

L RADIANT

CALORIC ACOUSTIC

ELECTRIC CHEMICAL

NUCLEAR

MECHANICALEnergy due to position

and motion; sum of potential and kinetic energies, including friction (heat, air resistance, etc).

POTENTIAL: Energy an object has because of its position.

KINETIC: is the energy of motion.

KINETIC ENERGYAll moving objects have kinetic energy.

It depends on MASS and SPEED.

m= mass (kg)v= object`s speed

EXAMPLESWhat is the kinetic energy of a car that has a mass

of 1200 kg and is moving at a speed of 20 m/s?

What is the kinetic energy of a car that has a mass of 2400 kg and is moving at 20 m/s? how does this kinetic energy compare to the kinetic energy of the car in the previous example?

What is the kinetic energy of a 4000 kg elephant that is running at 2 m/s? at 4 m/s? how do the two kinetic energies compare with one another?

EXAMPLESWhat is the kinetic energy of a 2000 kg bus

that is moving at 30 m/s?

What is the kinetic energy of a 3000 kg bus that is moving at 20 m/s?

POTENTIAL ENERGYNot all energy has to do

with motion.

Is the energy an object has because of its position.

GRAVITATIONAL POTENTIAL ENERGYWhen you lift an object, you do work on it.

You use a force that is against the force of gravity.

It depends on its WEIGHT and HEIGHT.

Weight = Newtons (N)Height = meters (m)

HEIGHT ABOVE WHAT?When you want to find out an object´s

gravitational potential energy, the ground that you measure the object´s height from depends on where it is.

EXAMPLEWhat is the gravitational potential energy of a book

with a weight of 13 N at a height of 1.5 m off the ground?

STEP 1: Write the equation for gravitational potential energy (GPE).

GPE

STEP 2: Replace the weight and height with the measurements given in the problem, and solve.

GPE = 13 N X 1.5 m

GPE = 19.5 N m = 19.5 J

EXAMPLESWhat is the gravitational potential energy of a

cat that weighs 40 N standing on a table that is 0,8 m above the ground?

What is the gravitational potential energy of a diver who weighs 500 N standing on a platform that is 10 m off the ground?

What is the gravitational potential energy of a diver who weighs 600 N standing on a platform that is 8 m off the ground?