Physics: Work, Energy and Power

The Forms of Energy

*heat energy *light energy *sound energy *nuclear energy *chemical energy *electrical energy *magnetic energy *mechanical energy: potential energy kinetic energy

What is a Machine?

A device which enables a force (the effort) acting at a point to overcome another force called the load acting at some other point.

Energy Transformation

A vast amount of energy is present around us; however it cannot always be used directly but may first have to be changed into more convenient forms. Large quantities are stored as chemical energy in fossil fuels and batteries, as nuclear energy in radioactive forms. These can be converted into more readily usable forms eg. heat, light and electricity NB: Thermal/Heat energy is always a by-product or product when dealing with energy transformation.

How to find Efficiency

Efficiency= useful energy output x 100% ------------------------------- energy input Efficiency= work done on load x 100% ---------------------------- work done by effort Efficiency= useful power output x 100% ------------------------------ power input

Law of Conservation of Energy

Energy can neither be created or destroyed but is merely changed from one form to another. In a system, energy input equals useful energy output + wasted energy. energy input= useful energy output + wasted energy.

What is Energy?

Energy is the ability to do work.

Fluid Pressure

Fluid Pressure in a liquid depends on the depth (h) of the liquid below the surface and on the density of the liquid.

Relationship between Pressure and Depth

If three similar holes are bored at different levels in a can which is filled with a liquid, the liquid spurts out fastest and furthest from the lowest hole. As depth increases pressure increases.

Efficiency - The Inclined Plane

If you push an object up a ramp or incline it requires less force than if you raise it straight up. So the input force is the force you use to push the object up or along the ramp, that is, the effort. The input distance is the distance you push the object up the ramp. The output force is the force you would have used if you lifted the object vertically to the same height without using the ramp, that is, equal to the weight of the load. the output distance is the distance you would have used if you lifted the object vertically to the same height.

What is Power?

Power is the rate at which work is being done or the rate at which energy is being supplied or converted

How to find Power

Power= energy converted/used ---------------------------------- time power= work done ---------------- time

What is Pressure?

Pressure is defined at the force acting (normally in a perpendicular direction) per unit area.

WATT

The S.I Unit of Power is WATT. One WATT is equivalent to one joule per second. One watt is the power of one joule per second.

PASCAL

The S.I Unit of Pressure is PASCAL. 1 Pascal is equal to 1 Nm

Joule

The S.I Unit of work and energy is the JOULE. One JOULE is the work done when a force of one newton moves its point of application on meter in the direction of the force. .:. 1J=1Nm

Efficiency

The efficiency of a machine is a measure of the useful energy output of a machine compared with the energy input. It is as the ration of useful energy output to the energy input.

Work and Energy

When work is done on a body or system, the body or system gains an amount of energy equal to the work done on it and this increases its capacity to do work. On the other hand, when work is done by a body or a system, it looses the amount of energy equal to the work done and it's capacity to do more work is decreased, as a result the work equation may be used to calculate energy transferred to or from the body or system involved.

What is Work?

Work is done when a force produces motion. The quantity or amount of work done by a force is given by the product of the force and the distance moved in the direction of the force. Work is said to be done and the point of application of a force moved. Work= Force x Displacement or Distance

How to find Kinetic Energy

kinetic energy= 1/2mass x the square of the velocity =1/2m(v squared)

How to find Potential Energy

potential energy=mass x gravity x height

How to Find Pressure

pressure= normal force (weight) -------------------------------- area P=F --- A

Potential Energy (Ep)

This is defined as the energy stored by a body or system of bodies by virtue of its position. Types of Potential Energy: *Gravitational *Elastic *Chemical

Gravitational Potential Energy

This is the amount of Potential Energy which a body gains or has owning to the work done in moving it against the gravitational attractions, to the earth.

Mechanical Energy

This is the energy acquired by objects in which work is done. Mechanical energy is then broken into two types: *Potential Energy *Kinetic Energy

Kinetic Energy (Ek)

This is the energy passed by a body by virtue of it's motion. A stationary body has no kinetic energy.

Efficiency

The principle of conversion of energy implies that the total energy output of a machine must be equal to the total energy input, however the work done by the machine or load is usually less than the energy input, this is because some of the input is usually wasted (converted into heat energy or sound) when work is done against forces such as friction.