ANCY C SIMONPhysical Science OptionalRegister Number- 13971004

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.

Sir Issac Newton

“If I have ever made any valuable discoveries, it has been owing more to patient attention, than to any other talent.”

-Sir Isaac Newton

Force• Force is an action that can change motion.– A force is what we call a push or a pull, or any

action that has the ability to change an object’s motion.

– Forces can be used to increase the speed of an object, decrease the speed of an object, or change the direction in which an object is moving.

Newton's Second Law• If you apply more force to an object, it accelerates at

a higher rate.

Newton's Second Law• If the same force is applied to an object with

greater mass, the object accelerates at a slower rate because mass adds inertia.

 

According to Newton, an object will only accelerate if there is a net or unbalanced force acting upon it. The presence of an unbalanced force will accelerate an object - changing its speed, its direction, or both its speed and direction.

Newton's second law of motion : 

Newton's second law of motion pertains to the

behavior of objects for which all existing forces are

not balanced. The second law states that the

acceleration of an object is dependent upon two

variables - the net force acting upon the object and

the mass of the object

 

The acceleration of an object depends directly upon

the net force acting upon the object, and inversely

upon the mass of the object.

As the force acting upon an object is increased, the

acceleration of the object is increased.

As the mass of an object is increased, the acceleration

of the object is decreased.

Newton's second law of motion can be formally stated as follows:

The acceleration of an object as produced by a net

force is directly proportional to the magnitude of the

net force, in the same direction as the net force, and

inversely proportional to the mass of the object.

Newton’s Second Law of Motion

In other words…

How much an object accelerates depends on the mass of the object and how much force is applied to it.

The equation for this is:

Force = mass x acceleration

F=ma

One Newton (1N) is the force required to produce an acceleration of 1m/s on a body of mass 1kg.

Units of Force = Newton (N)

SI units for mass is kg

SI units for acceleration is m/s2

1 Newton (N) = 1kg . m/s2

The unit of force is Newton(N)

Newton's Second Law

Three forms of the second law:

If a baseball is thrown at 150 m/s2 and its mass is 0.50 kg what force is necessary to change its direction?

a = 150 m/s2

m = 0.50 kgF = ?F = maF = (0.50 kg)(150 m/s2 )F = 75 kg m/s2

= 75 N

Newton’s Second Law of Motion

Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.

• We know that objects with different masses accelerate to the ground at the same rate.

• However, because of the 2nd Law we know that they don’t hit the ground with the same force.F = ma

98 N = 10 kg x 9.8 m/s/s

F = ma

9.8 N = 1 kg x 9.8 m/s/s

Applications of 2nd Law

Check Your Understanding Determine the accelerations that result when a 12-N net force is applied to

a 3-kg object and then to a 6-kg object.

A net force of 15 N is exerted on an encyclopedia to cause it to accelerate

at a rate of 5 m/s2. Determine the mass of the еncyclopedia.

Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is

tripled and the mass is doubled, then what is the new acceleration of the

sled?

Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is

tripled and the mass is halved, then what is the new acceleration of the

sled?

Your answers have to be: •   1. A 3-kg object experiences an acceleration of 4 m/s2. A

6-kg object experiences an acceleration of 2 m/s2.

2. Use F= m a with F = 15 N and a = 5 m/s2

So (15 N) = (m) x (5 m/s2) And m = 3.0 kg

3. Answer: 3 m/s2

The original value of 2 m/s2 must be multiplied by 3 (since a and F are directly proportional) and divided by 2 (since a and m are inversely proportional)

4. Answer: 12 m/s2 The original value of 2 m/s2 must be multiplied by 3

(since a and F are directly proportional) and divided by 1/2 (since a and m are inversely proportional)

Thank You