A Presentation By Mrs. Pooja P.Dani THE LAWS OF MOTION A Presentation By Mrs. Pooja P.Dani

Overview Force and Motion Balanced and Unbalanced Forces Types of inertia Newton’s First Law of Motion Newton’s Second Law of Motion Newton’s Third Law of Motion Principle Conservation of Momentum

Force and Motion The force is required to put a stationary body in motion or to stop a moving body. The force can be used to change the velocity of an object or direction of motion. The force can also change the shape of the body. When a we push, pull or heat an object we make a force to act on them, due to which we can bring the object in motion or can stop it. Force is a physical quantity that changes or tends to change the state of rest or of uniform motion of a body in a straight line. For Example: You might have seen a car in motion. We can stop the car by applying brakes which is nothing but a force applied on the car

Balanced and Unbalanced Forces If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. If they are not equal and opposite, then the forces are unbalanced and the motion of the object changes

Balanced and Unbalanced Forces A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion. Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

Inertia Inertia: the tendency of an object to resist changes in its state of motion Real Life example: We can explain the term inertia with the following example. Suppose we are traveling in a bus, and the bus suddenly starts moving we experience a jerk. When the bus is at rest our body is also at rest and as the bus starts its motion, the portion of the body which is in contact with the bus acquires velocity but the upper part of the body tries to remain at rest. So we fall back! The exact opposite situation occurs when moving vehicle suddenly stops by application of brakes.

Types of Inertia Inertia at Rest The inherent property of a body by virtue of which it can not change its position of rest, is called inertia of rest.

Types of Inertia Inertia of motion The inherent property of a body by virtue of which it can not change its state of motion, is called inertia of motion.

Types of Inertia Inertia of Direction The inherent property of a body by virtue of which it can not change its direction of motion, is called inertia of direction Below is a video which demonstrates the process of sharpening a knife and how sparks fly off tangentially during this process. http://www.ehow.com/video_4418693_sharpening-spade-drill-bit.html

Background Sir Isaac Newton (1643-1727) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion. He published them in his book Philosophiae Naturalis Principia Mathematica (mathematic principles of natural philosophy) in 1687. Today these laws are known as Newton’s Laws of Motion and describe the motion of all objects on the scale we experience in our everyday lives.

Newton’s First Law of Motion http://www.youtube.com/watch?v=iDGvBWmUcFU&feature=related In this video you can see the glass is placed on the paper. When we pull the paper at once, the glass remains steady on the table. This proves Newton’s First Law of motion. It states that… “Every inanimate body continues in its state of rest or of uniform motion in a straight line unless an external unbalanced force acts on it.” The first law is also called as Law of Inertia.

Newton’s Second Law of Motion http://zonalandeducation.com/mstm/physics/mechanics/forces/newton/newtonLaw2.html It states that… “The rate of change of momentum is directly proportional to the impressed force and takes place in the direction in which the force acts.”

Newton’s Second Law of Motion If a body of mass m moving with velocity u be subjected to force F acting in the direction of motion. Suppose v is the velocity of body after time t. The total initial momentum of body is mu and final momentum is mv after time t. Hence rate of change of momentum = change in momentum/time =(mv-mu)/t =m(v-u)/t =ma Hence rate of change of momentum is α F ma α F

Newton’s Third Law of Motion As you can see in this picture the rocket is being launched. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction. This is the demonstration of Newton’s Third law of motion.

Newton’s Third Law of Motion “To every action there is an equal and opposite and instantaneous reaction” Action and reactions are the terms explaining force.

Principle of conservation of momentum Just click the link given below. This is a small demo of principle of conservation of momentum. http://www.physicsclassroom.com/mmedia/momentum/cbb.cfm The principle of conservation of momentum states that – “If there is no net force acting on two interacting bodies then there total momentum is conserved.” In other word “If two freely moving bodies collide their total momentum after collision is the same as their total momentum before collision.”

Check Your Understanding 1. What acceleration will result when a 12 N net force applied to a 3 kg object?   2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass. 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?

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