Work is the scalar product of the force acting on an object and the displacement through which it acts. When work is done on or by a system, the energy of that system is always changed. If work is done slowly, we say that the power level is low. If work is done quickly, the power level is high. Kinetic energy is the energy an object has because of its motion, and potential energy is the energy an object has because of its location or configuration. If the energy of a system remains constant throughout a process, we say that energy is conserved.
W = F x d
Work is a measure of expended energy.
Work makes you tired.
Machines make work easy (ramps, levers, etc.)
Apply less force over larger distance for same work.
Work makes you tired.
Machines make work easy (ramps, levers, etc.)
Apply less force over larger distance for same work.
Definition
Heat – thermal energy that is transferred from one substance to another.
Thermal energy – the total energy of the particles in an object.
Sound – something audible; something that can be heard.
Chemical energy – the potential energy stored in chemical bonds.
Mechanical energy – kinetic or potential energy associated with the motion or position of an object.
Electrical energy – the energy of moving electric charges
Potential energy – the energy that is stored and held in readiness
Kinetic energy – the energy that an object has due to its motion
Electromagnetic energy – the energy of light and other forms of radiation
Nuclear energy – the potential energy stored in the nucleus of an atom.
What is Energy?
Energy is the ability to cause changes in matter and involves either motion or position, but that energy can be in many different forms. There are many forms of energy, such as heat, solar, chemical, mechanical, and electrical. Energy is the capacity to do work. Two main categories of energy.
Kinetic Energy: Energy of motion - A moving baseball can do work
Potential Energy: Stored (latent) capacity to do work.
Gravitational potential energy (perched on cliff)
Mechanical potential energy (like in compressed spring)
Chemical potential energy (stored in bonds)
Nuclear potential energy (in nuclear bonds)
Energy is the ability to do work, and when work is done, there is always a transfer of energy. Energy can take on many forms, such as potential energy, kinetic energy, and heat energy. The unit for energy is the same as the unit for work, the joule. This is because the amount of work done on a system is exactly equal to the change in energy of the system. This is called the work-energy theorem.
Kinetic Energy
Kinetic energy is the energy an object has because it is moving. In order for a mass to gain kinetic energy, work must be done on the mass to push it up to a certain speed, or to slow it down. The work-energy theorem states that the change in kinetic energy of an object is exactly equal to the work done on it, assuming there is no change in the object’s potential energy.
Kinetic Energy, KE = ½ MV2
Where,
M = mass in [kg],
V = velocity of object in [m/sec]
What are the units of KE?
[KE] = [mass] x [velocity]2 = [kg x m2/s2] == [Joule] or just, [J]
The work done on a system can also be converted into heat energy, and usually some of the work is.
Gravitational Potential Energy
Potential energy is the energy a system has because of its position or configuration. When you stretch a rubber band, you store energy in the rubber band as elastic potential energy. When you lift a mass upward against gravity, you do work on the mass and therefore change its energy. The work you do on the mass gives it potential energy relative to the ground. To lift it, you must apply a force equal to the weight mg of the mass through a displacement height h, and thus the work done in lifting the mass is
W = Fs = (mg)h
which must also equal its potential energy
PE = mgh
How much work does it take to lift a 50 kg suitcase onto the table, 1 meter high?
W = (30 kg) x (9.8 m/s2) x (1 m) = 490 J
Solar Energy
Solar Energy is the energy from the Sun, which provides heat and light energy for Earth.
Green plants use solar energy during photosynthesis to produce sugar, which contains stored Chemical Energy.
Heat Energy
Heat energy is the total energy of the particles that make up an object.
The faster these particles move, the higher the temperature of the object and the more heat energy it has. The Sun, material that is burning, and electricity are sources of heat energy. Transfer of heat energy can occur in three ways:
Conduction
Convection
Radiation
Chemical Energy
Chemical Energy is energy stored in particles of matter.
Chemical energy can be released, for example in batteries or sugar/food, when these particles react to form new substances
Electrical Energy
Electrical Energy is the energy flowing in an electric circuit.
A battery and generator are sources of electrical energy.
Mechanical Energy
Mechanical Energy is the energy due to the motion and position of an object. It is the total energy in a system.
Machines are a source of mechanical energy but so is falling water, or a human arm or leg.
Power
Work can be done slowly or quickly, but the time taken to perform the work doesn’t affect the amount of work which is done, since there is no element of time in the definition for work. However, if you do the work quickly, you are operating at a higher power level than if you do the work slowly. Power is defined as the rate at which work is done. Oftentimes we think of electricity when we think of power, but it can be applied to mechanical work and energy as easily as it is applied to electrical energy. The equation for power is
Power, P = Work/Time , W/t
and has units of joules/second or watts (W). A machine is producing one watt of power if it is doing one joule of work every second. A 75-watt light bulb uses 75 joules of energy each second.
Types of Energy
Energy can be broadly divided into two categories-
Renewable Energy
Renewable energy can be generated continuously practically without decay of source. E.g.- Solar Energy, Wind Energy, Geothermal Energy, Hydro Energy
Solar energy can be converted into electrical energy by using solar panels, or alternatively, be used as thermal energy using solar water heaters, solar cookers etc.
Wind energy can be converted into electrical energy by wind mills.
Geothermal energy exists inside earth crust. Natural hot water springs are a good source of getting such energy.
Using dams, water is allowed to pass through turbine blades, which produces electricity. In India, after coal, most of the energy is produced by this method.
Non Renewable Energy
Non renewable energy cannot be generated again and again, e.g. energy generated from combustion of fossil fuels, energy from coal and gas etc.
Energy is conserved. This means that energy cannot be created nor destroyed. If the total amount of energy in a system changes, it can only be due to the fact that energy has crossed the boundary of the system by some method of energy transfer.
Gasoline converts to energy which moves the car
A battery convert’s stored chemical energy to electrical energy
Dams convert the kinetic energy of falling water into electrical energy
The total amount of energy in the object or the system does not change when the type of energy changes from one form to another. This is known as the Law of Conservation of Energy.
This law is true for all types of energy transformations. Energy is only changed in form.
Conservative Forces versus Neoconservative Forces, and the Work
A force is said to be conservative if the work done by the force does not depend on the path taken between any two points. The gravitational force and the spring force are two examples of conservative forces. These two forces conserve energy during a round trip. A force is said to be non conservative if the work done by the force depends on the path taken. Friction is the most common example of a non conservative force on the AP Physics B exam, since a taking longer path will dissipate more heat energy. Work done by a non conservative force generally cannot be recovered as usable energy.
The Conservation of Mechanical Energy
When work is done on a system, the energy of that system changes from one form to another, but the total amount of energy remains the same. We say that total energy is conserved, that is, remains constant during any process. This is also called the law of conservation of energy.
We can use the fact that the sum of the potential and kinetic energies remains constant during free fall to solve for quantities such as speed or initial height.
The sum of the kinetic and potential energies of a system is called the total mechanical energy of the system. These same principles can be applied to a block sliding down a frictionless ramp, a pendulum swinging from a height, and many other situations. We could use Newton’s laws and kinematics to solve these types of problems, but usually conservation of energy is easier to apply.