Work, Energy, and Power

Work, Energy, and Power

What is energy? • Energy – the ability to do work. • Every source of energy you can think of fits the above definition. List three: • 1) __sunlight___ • 2) __heat________ • 3) __food_________

Work • What is work? • Work – Definition has 2 parts in physics. • 1) A force must have been exerted. • 2) The object being worked on must have moved or changed.

If I push the wall as hard as I can, is work being done to the wall? • No. • Thought process: • Did the wall move? Did the wall change? • If the answer to both of those is “no”, then no work was done.

If I push a desk around, was work done to the desk? Yes • If you sit in your desk to take a quiz, is work being done to the desk? No • If you squeeze a ball of play-doh, was work done to the play-doh? Yes • If you fold a piece of paper on the desk, was work done to the paper? Yes To the desk? No

There are 2 formulas for calculating work. • The first formula: W = F x d • W = work • F = Force • D = displacement. • Remember, the “W” is big, because little “w” means “weight.”

Force x displacement in units would be Newtonsx Meters • The Joule (J) is N x m. • Joule is our unit for work.

THE CATCH!!!!! • The force and displacement in the formula have to be in the same direction.

Is work done to the box when it’s pushed along the table? Yes • Is work done to the box when it’s picked up? Yes • Is work done to the box if I hold it? No • Is work done to the box if I hold it and walk to the left? No

The SECOND formula for Work is: • W = m x g x h. • W = work, m = mass, g = gravity, h = height. • Part of this formula is m x g. What was m x g the formula for? weight • So this formula can also be written as: • W = w x h.

W = F x d is for “mechanical work.” • Mechanical work is the work done by machines. • W = m x g x h is for “work against gravity.” • This is work done whenever the object is moved upwards, or against gravity.

Power • We compare strengths of work by comparing it’s Power. • We abbreviate this with a capital “P.”

Your formula for calculating Power is • P = W • T • Powers often compare different objects. • Example: Power for cars is measured in horsepower.

Inclined Plane • An inclined plane is a ramp that connects a upper level (usually the ground) to an lower level. • In fancy physics words, inclined planes turn work against gravity into mechanical work.

The W = F x d (mechanical work) is the work done by pulling/pushing something up the ramp. • The W = m x g x h (or W = w x h, work against gravity) would be done by lifting something without the ramp.

The mechanical work will ALWAYSequal the work against gravity in the calculations.

For the Lab • What were you doing work against when you were walking up and down the stairs?

Energy • Energy is the ability to do work. • That means energy causes forces that cause movement or change.

Work-Energy Theorem • BUT when work is done to matter it creates energy! • So energy creates work, and work creates energy. • This is called the work-energy Theorem.

Because of the theorem, both work and energy are measured in Joules. • An machine that creates mechanical work from energy is a motor. • An machine that creates energy from mechanical work is a generator.

Different Types of Energy! • Kinetic energy is energy from things in motion. • Potential energy is energy that’s being stored from objects at rest. • There are different types of these energies, too! Lets draw them!

Translational Kinetic Energy (KE) • Energy from motion.

Rotational KE • Energy from spinning.

Vibrational KE • Energy from vibrating.

Mechanical KE • Energy from gears moving or mechanical pieces working together.

Gravitational Potential Energy (GPE) • The energy something has before it falls.

Elastic PE • The energy something has when stretched out to go back to the way it was.

Chemical PE • The energy chemicals have to react.

Other forms of energy!Electricity • Electricity, like what’s from your plugs or lightning.

Thermal • Heat

Radiant • Light (like sunlight)

Nuclear • Energy from a nuclear chemical reaction, caused by fusion or fission.

To Calculate GPE • GPE = m x g x h. • GPE = Gravitational Potential Energy • m = mass • g = gravity • h = height • This is the same formula as the workagainst gravity formula!

Calculating Translational Kinetic Energy • TKE = ½ m x v2 • m = mass • v = velocity

Law of Conservation of Energy • Energy can neither be created nor destroyed. • Energy can go back and forth between potential and kinetic, but the total amount of energy will always be the same. • So when asked to find the total energy add all the numbers.

99.9% of energy for earth comes from sunlight. That causes all the wind, weather, ocean currents, photosynthesis, and the processes by which we get fossil fuels. Only .1% of earth’s energy comes from geothermal heat/volcanos, or earth’s rotation.

Work, Energy, and Power