Work and Energy

Energy (E) The ability to do work Energy is the fuel of an object. When work is being done on the object, the amount of fuel that the object has changes. This fuel can be expressed in many different ways.

Work (W) The energy transferred to an object by an applied force over a measured distance WORK is ENERGY TRANSFERRED

You can think of energy as … ▫The ability to do work ▫Work waiting to happen

A Kind of Kinetic Kinetic Energy ▫Energy of objects in motion

A Kind of Kinetic Thermal Energy ▫is the energy that makes things hot. It is a form of kinetic energy at the molecular level. Can you think of how heat or steam is used to do work?

A Kind of Kinetic Sound Energy ▫The vibration of sound waves traveling through a medium produces sound energy. At your last rock concert, could you feel the music?

A Kind of Potential Gravitational Potential Energy ▫is the energy stored in an object due to its height in an area where the force of gravity can act on it to make it fall.

A Kind of Potential Elastic Potential Energy ▫is the energy stored by the bending, stretching or compressing of matter

A Kind of Potential Chemical Potential Energy ▫is energy stored in the chemical bonds of matter and can be released by way of a chemical reaction, such as lighting a match. Can you think of an example of chemical energy release in the human body?

A Kind of Potential Radiant Energy ▫is carried by electromagnetic waves, like light. Radiant energy from the Sun can be transferred into heat to melt our snow. It can also move certain objects in a vacuum.

A Kind of Potential Nuclear Energy ▫is stored in the nucleus of every atom. An enormous amount of energy is released in a nuclear fission or fusion reaction.

A Kind of Potential Electrical Energy ▫is energy possessed by charged particles. The charges can transfer energy as they move through an electric circuit. We use electrical energy for many, many things!

A Kind of Potential 7. Magnetic Potential Energy is stored in the place between two magnets

What Kind of Energy? Kettle – demonstrates two forms of energy. What are they? Basketball – hold the basketball in front of you and then drop it. Theraband – stretch and release the theraband. What kind of energy is being stored in the theraband? Bicep Curls – perform some bicep curls and guess what form of energy is being accessed and produced.

What Kind of Energy? Lights – what kind of energy is being used to light the room? Magnets – can you feel the forces of attraction and repulsion? Solar Sail – read the article to find out what makes the solar sail fly. Stereo – put your hand near the speakers. Can you feel anything? Nuclear Power – do we use this in Canada? Rolling Cart – give the cart a push. What form of energy do you see?

Energy Transformation Equations Energy cannot be created or destroyed, only transformed from one type to another Energy transformation equations show how energy changes throughout a process Energy transformation equation for a microwave: electrical  radiant  thermal Arrows indicate a transformation

Create Energy Transformation Equations for: (simple) A child jumps on a trampoline A portable CD player operates with a battery An incandescent light bulb is switched on A rollercoaster climbs and descends the first hill A person playing an electric organ presses a key and we hear the note played

Create Energy Transformation Equations for: (complicated) A nuclear core heats up water to the boiling point which turns a generator Spring with a mass attached is pulled down and then released (moves up and down until it comes to a rest on it’s own) A match is struck against a matchbox and ignites

Work-Energy Equivalence In general, doing work gives an object energy AND an object that has energy can do work. Both Energy and Work have the unit Joule (with a capital “J” = N.m)

Conditions for Work 1. A force must be exerted on an object 2. The object must be displaced (moved) by the force 3. At least part of the force must be in the same direction as the displacement

Examples A person lifting a box from the floor to the table A person pushing a box along the floor from one spot to another

What is Work? In Physics, work has a very specific definition Is this work? ▫Video (BBT)

Work Energy transferred to an object over a distance WORK IS ENERGY GAINED OR LOST

What if we push the box 16m?

What if the mass of the bucket was 40kg?

Positive Work When the force is in the same direction as the displacement "+" work = force tends to increase the energy of the object

Negative Work If the force is opposite to the direction of the displacement (i.e. friction) "-" work = force tends to decrease the energy of the object

Example A 42 kg child runs and then slides 7.8m along an iced over pond. The coefficient of kinetic friction between the child's boots and the ice is a.) What is the force of kinetic friction acting on the child? F K = μ K F N F N = Fg = mg =(42kg)(9.8m/s2) = 4.1 x 10 2 N F K = (0.0050)(4.1 x 10 2 N) = 2.1N

Example Continued b.) Calculate the work done by the kinetic friction W = F∆d = (-2.1N)(7.8m) = -16 J

Who thinks they can do zero work?

Zero Work but a force is applied ▫a student holding another student on their shoulders F=0 but displacement occurs ▫a puck on an air table (no friction) F ▫a javelin thrower runs with the javelin above their head FaFa

Challenge Question Who will do more work? A.) 2 people lifting a piano into the back of a truck OR B.) 2 people pushing the same piano up a ramp to the back of the same truck

Work and Energy problem set