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Newton's Laws of Motion

Sky fall Sky fall As the skydiver falls and accelerates downwards, he gains speed with time. The increase in speed is accompanied by an increase in air resistance. This force of air resistance counters the force of gravity. As the skydiver falls faster and faster, the amount of air resistance increases more and more until it approaches the magnitude of the force of gravity. Once the force of air resistance is as large as the force of gravity, a balance of forces is attained and the skydiver no longer accelerates. Then the skydiver is said to have reached a terminal velocity. When all the sky divers attain the terminal velocity they will be able to form a circle, which is an interesting phenomenon. Lets learn more of such interesting concepts in this topic.

Learning Objectives

After completing the topic, the student will be able to:

  • Identify the types of forces that are encountered in day-to-day life.
  • Appreciate and apply Newton's first law of motion and explore its implications in daily life.
  • Distinguish between mass and weight with relevance to a physical entity.
  • Appreciate and apply Newton's second law and explore its implications related to everyday life.
  • Understand and distinguish clearly between static and dynamic equilibrium.
  • Explore Newton's third law using its practical applications as observed in daily life.
  • Understand the normal force and apply it in daily life.
  • Discuss friction, types of friction and apply them to get clarity about various concepts like magnetic levitation, etc.
ball and paper Newton's laws of motion Man pushing a wheelbarrow to demonstrate Newton's three laws of motion. The first law states that an object will either remain at rest or move at a continuous speed, unless acted upon by a force. The second law states that the force of an object is equal to its mass times its acceleration. The third law states that when one object places a force on a second object, the second object places a force of equal strength in the opposite direction on the first.

When we discussed linear motion, we described terms such as displacement, velocity and acceleration. But we did not ask: what causes motion? Surely objects in motion are moving due to something? We also said that no object really is at rest. What is the meaning of all this? What exactly is a state of rest ? To answer these important questions, we have to first understand a physical entity called force. The relationship of motion to the forces that cause it is the subject of Dynamics whereas Kinematics is the language of describing motion.

We use two concepts, force and mass to analyze the principles of dynamics. These principles can be summarized in three statements called Newton's laws of motion. The first law states that when the net force on the body is zero, its motion does not change. The second law relates force to acceleration when the net force is not zero. The third law is a relationship between the forces that two interacting bodies exert on each other.

These laws are a synthesis of ideas, observations and results of various experiments conducted by Newton and many other scientists before him including Copernicus, Brahe, Kepler and Galileo. Newton's laws are the foundation of classical mechanics and they help us understand most of the familiar kinds of motion. Newton's laws need to be modified in situations involving speeds close to the speed of light or very small size such as subatomic particles.

Push or Pull Push or Pull In physics, force is a push or a pull that changes or tends to change the state of rest or uniform motion of an object or changes the direction or shape of an object.
Bat changes the direction of the ball Batsman applies some force to change the direction of the ball.
Force and interactions

A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. Hence we can say that pushes and pulls are forces. Whenever we are pushing or pulling, lifting or bending, twisting or tearing, stretching or squeezing, we are exerting a force.

i. Opening and closing a door.
ii. A ball being pushed.
iii. A train engine pulling the train coaches.
iv. A spring being stretched.
v. A tooth paste being squeezed.

Effects of force: It is not easy to understand the concept of force, because force cannot be seen; but its effect on objects can be observed and measured. In everyday terms, force can be seen in action when an object is pushed, pulled, stretched or squeezed. We observe that changes in motion like speeding up, slowing down and changing direction are due to the effects of forces.A force can produce the following effects:

1. A force can move or stop a body.
2. A force can change the speed of a body
3. A force can change the direction of a moving body.
4. A force can change the shape or size of a body.

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