Work• It is defined as the product of the force applied upon an object and the distance that the object is moved in the direction of the force.
• For work to be done, two things must occur: 1. You must apply a force to an object. 2. The object must move in the same direction as the force you apply.
• Example1:A force of 12 Newton acts on an object over adistance of 15 meter. What is the work in Nm?
Unit of Work• Another common unit of energy is the calorie. 1 calorie (cal) is equal to 4.18 joules (J). 1cal = 4.18 J
Examples:• Example2:An object is pulled 4 m on a horizontal surfaceby applying a force of 50 N. Calculate the workdone on the object.• Example3:A boy pushes a box for 50 m on a frictionlesssurface and he does a work of 10000 J. Find theforce that he applies to the box.
What is energy?• It is the ability to do work.• We do work by using energy, so we can say that work and energy should have the same units: joule (J).
TYPES OF ENERGY• Potential Energy: It is the energy of an object due to its position.• By raising an object from the ground to a height h, we change its position, by applying a force at list equal to its weight. So we do work against the force of gravity. The work done on the object is stored as potential energy.
Example:• A man lifts up a 4.5 kg box on to a table which is 120 cm high. How much potential energy does the box gain? (g= 10 N/kg)
• Kinetic Energy: It is the energy of an object due to its motion.• Kinetic energy (EK) of an object of mass m moving at a speed v and is given as;
Example:• A cyclist has a mass of 43 kg and his bicycle weighs 7 kg. If the cyclist moves with a speed of 4 m/s in the forest, what will his kinetic energy be?
• Mechanical energy: It is the total amount of potential and kinetic energy in a system. Mechanical energy=potential energy + kinetic energy