Work

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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 a distance 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 surface by applying a force of 50 N. Calculate the work done on the object. • Example3: A boy pushes a box for 50 m on a frictionless surface and he does a work of 10000 J. Find the force that he applies to the box.

Energy

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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