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Energy can be described as the ability that objects have to change themselves or inflict change into other objects. These changes can range from temperature, speed, pressure, position, etc, and can be either physical or chemical. Energy is measured in joules (J), which represent the energy required to push with a force of 1 newtons for a distance of 1 meter (1 newton-meter).

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Energy is never created or destroyed. It only changes forms. It can be though of as a sort of currency that can be spent and invested into something else or saved. It takes energy to "invest" in a change like speeding up. Opposite changes like slowing down "release" energy.  Some forms of energy include kinetic energy, potential energy, mechanical energy, electric energy, magnetic energy, chemical energy, nuclear energy, elastic energy, pressure energy, sonic energy, radiant energy, and thermal energy.

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The basic metric unit of energy is the joule (J). Electrical energy is usually measured in kilowatt-hours (kWh). A more commonly used unit of energy is the food Calorie. The food Calorie is the exact amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. The British thermal unit (Btu) measures heat energy. It is the amount of energy required to raise the temperature of 1 pound of water by 1 degree Celsius.

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RollerKinetic energy is energy of motion. A moving ball has kinetic energy because it can cause change in the motion of other objects. Kinetic energy can change directly into potential energy. If a ball is tossed up, there is only potential energy when the ball reaches the highest point. While the ball is on its way to the highest point, the kinetic energy changes into potential energy. The following shows an example of the usage of the kinetic energy formula (Ek = (1/2)mv²: a rollercoaster has a mass of 500kg and is traveling at a speed of 20m/s. The kinetic energy of the roller coaster is 100,000 J.

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Potential energy is energy due to the object's position. Objects with potential energy have the ability to exert forces and transfer energy. Gravitational potential energy describes the potential energy of an elevated object. For instance, a vase is located at the top of a shelf. The cabinet is 5 meters high and the vase weighs 6kg. If we follow the formula for potential energy, we can tell that the vase has a potential energy of 294 J.

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Friction and the Law of Conservation of Energy

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Friction and the Law of Conservation of Energy

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When friction is not present, a ball would roll forever (due to Newton's law of inertia). When friction is present, however, the ball's kinetic energy would decrease and it will slow down. The force of friction is turning kinetic energy into thermal energy and wear. Both potential and kinetic energy are not available, but that doesn't mean it was destroyed.

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Work is the energy transfer that occurs because of a force exerted over a distance. Work means energy transfer between objects. This means if you stretch a rubber band, then you are transferring energy that the rubber band will then store as elastic potential energy. When you push an object 2 meter away with a force of 2 newtons, you are doing 4 joules of work. For example, if a ball is thrown 75 meters away with a force of 4 newtons (4 N * 75m), the work being done is 300 J.

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To lift something off a surface, you must apply a force equal to the object's weight. The work done in that situation is equal to its change in potential energy. Work done against gravity is equal to weight multiplied by change in height. The path that is taken by the object does not matter because work is done by the part of the force that acts in the direction of the motion. For example, when taking a box up a set of stairs, only the vertical distance will matter when doing work, because gravity only acts vertically.

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Every process transforming energy can be thought of as a machine. The work input is the amount of energy supplied to the machine, while the work output defines the work or energy coming out of the process. For example a rope and pulley may be used to lift a load of 10 N with a work input of 10 J (5 N * 2m), then the work output will also be 10 J, but the 10 N load will only be carried 1m
(10 N * 1m). The fact that both the input and output of this process were equal is an example of the law of conservation of energy.

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The efficiency of a machine describes the ratio of its work input to its work output. For example, an average car's efficiency is 13% as only 13% of the work input is used to actually move the car. Most of it goes to waste heat. To calculate efficiency, divide work input by work output.

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Power is the rate at which work is done, or how fast energy is transferred to an object. Power is measured in watts (W). One watt is equal to 1 joule per second. A street car's power is around 112,000 W, while a sports car's power exceeds the numbers of 560,000 W.

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A machine is a device that uses moving parts that cooperate to accomplish a goal. The work input in this case would be everything you do to make the device accomplish its task, and the output would be the task being accomplished. Because of that, the inputs and outputs can be force, energy, or power. A simple machine describes a unpowered machine that accomplishes its task with only one movement.

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Mechanical advantage is the ratio of input force to output force. If the mechanical advantage is greater than 1, than that means the output is greater than the input. If the mechanical advantage is equal to 1, then the output is equal to the input.

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A lever is a stiff structure that rotates around a point (fulcrum). The fulcrums, input arms and output arms of a lever are all adjustable, and therefore, so is the mechanical advantage. There are three types, or classes, of levers. The 1st-class lever shows both arms on the sides of the fulcrum. The 2nd-class lever shows a lever with one arm and the input force is being applied on the farther side of the lever. Finally, the third-class lever has one arm and has its input force being exerted on the closer side of the arm. The mechanical advantage of a first-class lever can be calculated by dividing the length of the input arm length by the output arm length.

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Gears can transfer motion and force when the teeth of one gear presses and pushes on another gear while rotating. They can also multiply forces and change rotation speed. The input gear is the one the force input is applied to while the output gear is the one connected to the output of the machine. The gear ratio describes the ratio of the turns of the output gear to the turns of the input gear. This gear ratio is also equal to the number of teeth on the input gear divided by the number of teeth on the output gear. The mechanical advantage of the gears is the inverse of the gear ratio.

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A pulley is a machine consisting of a wheel and rim around the wheel to hold a rope. When an input force is applied on one side of the pulley, an output force can be created in another direction. The mechanical advantage of a rope/pulley is based on how many strands of rope are supporting the wheel.

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The inclined plane, or ramp, allows you to raise a heavy object without lifting it. Its mechanical advantage can be calculated by dividing the ramp length by the ramp height. Ramps reduce input force by increasing the distance by which the input force acts.

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A wedge can be considered a ramp that works while in motion. It has a side that slopes down to a thin edge. Its mechanical advantage is inversely related to the size of the wedge angle. Sharp wedges cause large forces. A knife can cut through food easily. If the surface of the wedge is rough, then it can stop forces.

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A wheel rotates around a rod called an axle. The wheel and axle can move together to lift a load or travel. Its mechanical advantage can be calculated by dividing the wheel's radius to the radius of the axle. Some wheel/axle systems used everyday are cars, bicycles, doorknobs, etc.