Dynamics: Intro

Physics 11

What is dynamics?

area of Physics Is the branch of mechanics concerned

with the forces that cause motions of bodies What is a body? physical body or physical object (usually

called a body or object) is a collection of masses taken to be one. For example, a basket ball can be considered an

object but the ball also consists of many particles (pieces of matter).

Force = push or pull

How are kinematics and Dynamics related? The study of the causes of motion and

changes in motion is dynamics. In other words the study of forces and why objects are in motion.

In contrast kinematics, describes only the motion of objects without consideration of the causes leading to the motion.

This guy named Newton….

1643 – 1727 Started the groundwork for most

of classical mechanics. Newton described universal

gravitation and the three laws of motion which dominated the scientific view of the physical universe for the next three centuries.

Newton showed that the motions of objects on Earth and of celestial bodies are governed by the same set of natural laws by demonstrating the consistency between Kepler's laws of planetary motion and his theory of gravitation, thus removing the last doubts and advancing the Scientific Revolution.

We’ll come back to Newton….

But first Galileo: He, like many, attempted to understand why objects move or remain at rest

Galileo…

His experiment challenged the commonly held belief, at that time, that an object motion was the result of a continued force Instead, he viewed motion as a state just as natural as rest

He had identified the natural tendency of mass to continue what it is already doing…continue in motion or stay at rest He was defining inertia, he ideas were not immediately

accepted but his concepts of inertia have stood the test to time!

Inertia:

Is the natural tendency of an object to remain in its current state of motion

The amount of an objects inertia is directly related to its mass.

“An object in motion will remain in motion or an object at rest will remain at rest until acted upon by an external force.” Newton’s First Law

Inertia = Mass

Bigger masses have more…

Smaller masses have less inertia.

Which is harder to stop?

The larger mass has more inertia. It has more resistance to changes in motion!

Practise:

Pg 129 #1, 2, 3, 4