Energy is a property that objects or systems have, which allows them to accomplish work or to produce heat, light, or other forms of radiation. In physics, energy is defined as the ability to do work, meaning the capacity to move objects against a force, create motion, or produce a change in a system. Energy can be classified into different types, such as kinetic energy, potential energy, thermal energy, electromagnetic energy, and nuclear energy.

**Table of Contents **

**Kinetic Energy**

Kinetic energy is the energy associated with the motion of an object. The formula for kinetic energy is $KE= 0.5mv^2$, where m is the mass of the object and v is the velocity. For example, a ball with a mass of 1kg is thrown with a speed of 10m/s. The kinetic energy of the ball would be $KE= 0.5(1)(10^2) = 50J$. This means that the ball has 50 joules of energy due to its motion.

**Potential Energy**

Potential energy is the energy associated with the position or configuration of an object. There are different types of potential energy, such as gravitational potential energy and elastic potential energy. Gravitational potential energy is the energy that an object possesses due to its height above a reference point. The formula for gravitational potential energy is $PEg=mgh$, where m is the mass, g is the acceleration due to gravity $(9.81m/s^2)$, and h is the height. For example, a book with a mass of 1kg is on a shelf 2 meters above the ground. The gravitational potential energy of the book would be $PEg=(1)(9.81)(2) = 19.62J$, which means that the book has 19.62 joules of energy due to its height.

**Elastic Potential Energy**

Elastic potential energy is the energy stored in an object when it is deformed, such as a spring or a rubber band. The formula for elastic potential energy is $PEs= 0.5ks^2$, where k is the spring constant and s is the displacement of the spring from its equilibrium position. For example, a spring with a spring constant of 10N/m is compressed by 0.2 meters. The elastic potential energy of the spring would be $PEs= 0.5(10)(0.2^2) = 0.2J$, which means that the spring has 0.2 joules of energy stored in it.

In conclusion, energy is a crucial concept in physics that describes how objects or systems have the ability to do work or produce different forms of radiation. Kinetic energy is related to the motion of an object, while potential energy is related to its position or configuration.

**Example Questions:**

**1. What is the kinetic energy of a car with a mass of 1200kg that is traveling at a speed of 25m/s?**

**Solution:** $KE= 0.5mv^2 = 0.5(1200)(25^2) = 750,000J$

Therefore, the kinetic energy of the car is 750,000 joules.

**2. A 50kg object is lifted 5 meters vertically against the force of gravity. What is the gravitational potential energy of the object?**

**Solution: **$PEg= mgh = (50)(9.81)(5) = 2452.5J$

Therefore, the gravitational potential energy of the object is 2452.5 joules.