forms of energy

Forms of Energy

Science 10

Topics covered today

Outline of today’s lesson:• What is Energy?• Heat and Energy• Different forms of energy

– Chemical– Electrical and Magnetic– Nuclear and Solar

• What is Potential and Kinetic Energy?

What is Energy?

• What do you think Energy can do?

What is Energy?

• What do you think Energy is?

What is Energy?

• Energy is defined as the ability to do work, which may involve moving an object at rest into motion or changing the velocity of an object already in motion.– This change in motion, does not have to be at

the macroscopic scale. In fact, most forms of energy that cause the motion of objects occur at the atomic level. They deal with atomic or molecular movement.

Heat and EnergyI bet that when you are sitting in front of a fireplace or a campfire, you can tell that heat is present. But how does that energy get from the fire to you?

• So, what is heat?– Heat is the transfer of thermal energy from a

warmer object to a cooler object.• Great, now what is thermal energy?

– Thermal energy is the movement of particles within a substance.

– All forms of energy can be converted to thermal energy.

Law of Conservation of Energy

• The Law of Conservation of Energy states that:– Energy is neither created nor destroyed, it

can only change from one form to another.• Examples of this at work are:

– Hydrocarbon combustion turns chemical energy into thermal and kinetic energy.

– The chloroplasts in plants turn solar energy into chemical energy by forming glucose and oxygen gas from carbon dioxide and water.

Different Forms of Energy: Chemical

• Chemical Energy is the potential energy stored in the chemical bonds of compounds.– This form of energy is released into the

environment during combustion reactions to produce heat. (exothermic)

– This form of energy is produced during photosynthesis from solar energy.

– Different compounds and reactions have (and will produce) different amounts of chemical energy and either release or absorb heat.

Different Forms of Energy: Electrical and Magnetic

• Electrical Energy is the work done by moving charges (electrons).– Volta proved that there was a connection

between chemical and electrical energy when he invented the first battery in early 1800’s.

– Other scientists discovered a similarconnection between electricity andmagnetism and heat and electricity.

– Edison found the connection betweenlight and electricity with his inventionof the light bulb.

Different Forms of Energy: Nuclear and Solar

• Nuclear Energy is the potential energy stored in the nucleus of an atom. When a nucleus is split (fission) or when two nuclei combine (fusion) this energy is released.– Solar Energy is produced by the fusion of two

hydrogen atoms to form a helium atom.– The amount of energy released through

hydrogen fusion is about 1,000,000 times greater then the amount of energy released by the combustion of hydrogen.

What is Potential Energy?

• There are two types of energy that can be observed in nature: potential and kinetic.

• Potential energy relates to an object’s ability to do work. The only form we deal with in this course is gravitational potential energy.– Gravitational Potential Energy is directly

related to how high an object is above the Earth’s surface.

– The farther an object falls, the more work it is capable of doing.

Gravitational Potential Energy

• The formula for Gravitational Potential Energy is:

– Where E is the potential energy in joules (J).– Where m is the mass of the object in kilograms.– Where g is the acceleration of gravity in m/s2.

On Earth, g = 9.81 m/s2. – Where h is the vertical distance from the ground

in meters.

E = mgh

What is Kinetic Energy?

• Kinetic energy is the ability to do work through an object’s motion. (Energy of motion)– Gravitational Potential Energy is

transformed into kinetic energy as an object (that is released) accelerates towards the ground.

– The SUM of the kinetic and potential energy of an object is called its mechanical energy. It is a topic that we will save for later.

Example problems

1. Ashley has a 20kg television perched on his TV stand. It sits 1.1m above the floor. Calculate the TV’s gravitational potential energy relative to the floor.

Example problems

1. Ashley has a 20kg television perched on his TV stand. It sits 1.1m above the floor. Calculate the TV’s gravitational potential energy relative to the floor.

Example problems

2. The gravitational potential energy relative to the ground of a 6.1kg owl is 1260J. How far from the ground is the owl perched?

Example problems

2. The gravitational potential energy relative to the ground of a 6.1kg owl is 1260J. How far from the ground is the owl perched?

Example problems

3. A weightlifter hoisted a barbell 1.90m off the ground and held it there momentarily. The gravitational potential energy of the barbell equaled the work input of 1600J. What is the mass of the barbell?

Examples

Example problems

4. An object with a mass of 1.80kg is on top of a table that is 0.750m off the floor. The object is raised off the tabletop and held there.

– What is the gravitational potential energy in relation to the tabletop?

– What is the gravitational potential energy in relation to the floor?

Examples

Examples:

• Example:

Hydroelectric Power Plants generate their electrical energy by harnessing the gravitational potential energy of water falling from a higher to a lower elevation. What mass of water needs to fall from a height of 85 m to generate 1 MJ (1,000,000 J) of energy?

Examples

Homework

Forms of Energy• Check and Reflect: p172

– Questions 12, 13 and 14

Gravitational Potential Energy• Practice Problems: p174 – 175

– Questions 1, 2, 3• Check and Reflect: p178

– Questions 4, 5, 6

Elastic Potential Energy

• The other common form of potential energy that we deal with in Science 10 is elastic potential energy or Ep(elastic). This is the form of energy stored in a stretched or compressed spring or elastic. The formula is:

•  Ep(elastic) = Fd

• - Where Ep(elastic) is the elastic potential energy in joules (J).

• - Where F is the force exerted on the elastic object in newtons (N).

• - Where d is the distance the material is stretched or compressed in m

Examples

• An elastic cord is stretched 240 cm and is storing 3000J of elastic energy. What is the force being exerted on this cord?

• Zach decided that he was going to go bungee jumping at the WEM waterpark. If Zach weighs 63 kg and he is 30 m above the water, how far will he fall IF the elastic force of the bungee cord is 620N? Will he hit the water?

Examples

Examples

Kinetic Energy:

• The energy of an object in motion.

• Ek = mv2

•  - Where Ek is the kinetic energy of the object in joules (J).

•  - Where m is the mass of the object in kilograms.

•  - Where V is the velocity of the object in m/s.

How to Isolate m and v

isolate m and v

ExamplesHow much kinetic energy is stored in a 3kg toy truck moving at 2.5m/s?

How much kinetic energy is stored in a 1400kg car moving at 90km/h?

Examples

ExamplesWhat is the speed of a mini-submarine that has the kinetic energy of 225000J and a mass of 500kg?

What is the mass of a sprinter that has a kinetic energy of 5100J and a speed of 10.8m/s?

Examples

Practice

• B2.3: Practice Problems: (p179 - 181)•  - Questions 5, 6 and 7 --> On kinetic

energy

• B2.3: Check and Reflect: (p182)•  - Questions 2, 5, 6 and 7 --> On kinetic

energy