

Speed Velocity Acceleration Constant Acceleration Free Fall Forces and Newton's Law Kinetic Energy Potential Energy Free Fall Forces Conservation of Energy Conservation of Momentum PHYSICS LINKS Thinkquest Physics LibraryPhysics Zone Multimedia Physics Studio 
Forces and Newton's Laws When physicists talk about force they mean a push or a pull. In many sports, such as football, hockey, basketball, and tennis, in order to launch a shot players push or pull on a ball or similar object. Newton's Laws are concerned with exploring the amount of force that is required to move any object and how the force changes with variation in the mass of the object and acceleration applied. Newton established the relationship between force and mass. He observed that the amount of force that is needed to move an object is directly proportional to the mass of the object. For example, if we wish to move a pen and a book, greater force would be required to move the book because it is heavier than the pen. Newton's First Law In physics the three major laws concerning forces are called Newton's laws because they were established by Isaac Newton during the seventeenth century. The first law is called the law of inertia: An object continues in its state of rest or motion at constant velocity
unless there is a net force (sum of all forces that act on the body)
that has been applied to this object.
Books on a table at rest
If a book is simply lying on a table in a state of rest then the sum of all forces that act on that book is equal to zero. When we remove this book from the table we exert a force on the book and change its state of rest to a state of motion. The greater the mass of the book the greater the force that we have to apply to the book in order to change its state from rest to motion. The natural tendency of any object that is not being moved is to be at rest. However it is important to note that the net force that acts on an object when it is at rest (zero) is equivalent to the net force when it is in motion and maintaining a constant speed. The term inertia describes the natural tendency of any object to be in a state of rest or in a state of motion at constant velocity when the net force on the object is equal to zero. Newton's Second Law Newton's First Law describes the concept of inertia and the ability of a body to continue to stay in a state of rest or to move with a constant velocity. In both cases the net force exerted on the body is zero. The Second Law deals with situations where the net force is not equal to zero anymore and the velocity of a body starts changing. By performing experiments Newton concluded his Second Law: The acceleration is directly proportional to the net force and inversely proportional to its mass. For instance, the same force applied to a child's wagon produces a greater acceleration than when applied to a car.
Comparison of a man pushing a child in a wagon and a man pushing a car
The acceleration always points to the direction of the net force.
Solution: Step 1:
Step 2: Plug the data into the formula given above and solve the problem: F = 15 kg 20 m/s^{2} = 300 N Answer:
The net force being exerted on a body is 300 N.
Problem: Hockey player hitting a puck
Solution: Step 1: In this problem we are given the following: m = 163 g (.163 kg) Step 2: Plug the data into the formula given above and solve the problem: 20 N = .163 kg x a
a =123 m/s^{2}
Solution: Step 1: In this problem we are given the following: F = 20 N
a = 5m/s^{2} Step 2: Plug the data into the formula and solve the problem: 20 N = m 5m/s^{2}
m = 4 kg Answer: The mass of the object is 4 kg. 