Newton’s LawsPhysics 113 Goderya

Chapter(s): 5Learning Outcomes: All

Force

Force: It is a push or a pull.

Force has both magnitude and direction.

Force exist in a variety of situations.

Types of Forces

• Contact Forces: Force is due to physical contact between the bodies. Example mechanical forces.

• Field Force: No physical contact is necessary to experience the force. Examples are Gravitational, Electrical, Magnetic, and Nuclear Forces.

A New Era of Science

Mathematics as a tool for understanding physics

Isaac Newton (1643 - 1727)

• Building on the results of Galileo and Kepler

Major achievements:

1. Invented Calculus as a necessary tool to solve mathematical problems related to motion

• Adding physics interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler

2. Discovered the three laws of motion

3. Discovered the universal law of mutual gravitation

A New Era of Science

Mathematics as a tool for understanding physics

Isaac Newton (1643 - 1727)

• Building on the results of Galileo and Kepler

Major achievements:

1. Invented Calculus as a necessary tool to solve mathematical problems related to motion

• Adding physics interpretations to the mathematical descriptions of astronomy by Copernicus, Galileo and Kepler

2. Discovered the three laws of motion

3. Discovered the universal law of mutual gravitation

Newton’s Laws of Motion (1)

1. A body continues at rest or in uniform motion in a straight line unless acted upon by some net force.

An astronaut floating in space will continue to float forever in a straight line unless some external force is accelerating him/her.

Newton’s Laws of Motion (2)

2. The acceleration a of a body is inversely proportional to its mass m, directly proportional to the net force F, and in the same direction as the net force.

a = F/m F = m a

Newton’s Laws of Motion (3)

3. To every action, there is an equal and opposite reaction.

The same force that is accelerating the boy forward, is accelerating the skateboard backward.

M = 70 kg

m = 1 kg

v = 7 m/s

V = ?

The Universal Law of Gravity

• Any two bodies are attracting each other through gravitation, with a force proportional to the product of their masses and inversely proportional to the square of their distance:

F = - G Mm

r2

(G is the Universal constant of gravity.)

Gravity and Distance: The Inverse-Square Law

Inverse-square law• relates the intensity of an effect to the inverse-

square of the distance from the cause• in equation form: intensity = 1/distance2

• for increases in distance, there are decreases in force

• even at great distances, force approaches but never reaches zero

Inverse-Square Law

Inverse-Square Law

Universal Gravitation

Universal gravitation• everything attracts everything else

example: Earth is round because of gravitation—all parts of Earth have been pulled in, making the surface equidistant from the center

• The universe is expanding and accelerating outward.