Energy is defined as the ability to do work. It is not a type of matter or a measure of time, and it differs from force.

Kinetic energy is the energy of motion, which is why a moving car is a prime example. The other options involve objects at rest or storing potential energy.

The law of conservation of energy states that energy cannot be created or destroyed; it can only be transferred or transformed. This fundamental principle underlies all energy transformations.

When you rub your hands, the kinetic energy from the motion is transformed into thermal energy because of friction. This is why your hands warm up during the process.

Wind energy is renewable because it is naturally replenished and virtually inexhaustible. In contrast, fossil fuels, natural gas, and nuclear energy depend on finite resources.

Food contains chemical energy stored in its molecular bonds. When you digest food, this energy is converted into other forms such as motion and heat.

Most power plants convert energy from nuclear reactions or fossil fuels into mechanical energy, which then drives turbines to produce electrical energy. This multi-step conversion process is fundamental to electricity generation.

The joule is the standard SI unit for measuring energy. In contrast, a watt measures power, a newton measures force, and a pascal measures pressure.

A pendulum continuously transforms gravitational potential energy into kinetic energy and then back into potential energy as it swings. This cyclical transformation exemplifies energy conservation in mechanical systems.

Solar energy is the radiant energy that comes from the sun. It can be harnessed with solar panels to produce electricity and heat.

Renewable energy sources such as solar and wind are beneficial because they are naturally replenished and generally have a lower environmental impact. However, they can be intermittent and sometimes costly to install initially.

Combustion is the process by which fuel is burned to release energy. This released energy is then converted into mechanical energy that powers the car.

Energy is conserved in an isolated system where it merely shifts from one form to another without any net loss or gain. This is the basis of the law of conservation of energy.

A major challenge with wind energy is that not all regions experience consistent wind speeds. The variability in wind can limit the efficiency and reliability of wind turbines.

In a battery-operated flashlight, the battery's stored chemical energy is first converted into electrical energy, which then powers the bulb to produce light (radiant energy). This series of conversions is essential for the device's function.

Friction between surfaces causes some of the kinetic energy of a moving object to be converted into thermal energy (heat). This conversion is one reason objects eventually slow down.

When you lift an object, you are doing work against gravity, which increases the object's gravitational potential energy. This stored energy can later be converted to kinetic energy if the object is dropped.

Increasing efficiency means that a larger fraction of the input energy is converted into the desired form of work rather than being wasted. It is a key goal in engineering energy devices.

The human body converts the chemical energy stored in food into mechanical energy (for movement) and thermal energy (to maintain body temperature). This demonstrates how energy is continuously transformed to meet biological needs.

At the highest point of its trajectory, the ball's speed is zero, meaning its kinetic energy is at a minimum while its gravitational potential energy is at its maximum. This is a classic example of energy transformation between kinetic and potential forms.