The History of Dynamics

The History of Dynamics

• All science was based on the teachings of the ancient Greek philosophers

• Aristotle taught that there was natural and unnatural motion for objects

• Unnatural motion is the result of a force; natural motion leads to the object’s natural place on Earth

• More massive objects fall faster than less massive objects

The History of Dynamics – Galileo

• Then along comes Galileo, born near Pisa, Italy, 1564

• The musket ball and cannon ball experiment

• 1638, Galileo published a book called Discourses and Mathematical Demonstrations Relating to Two New Sciences

• The basis of modern science – described falling bodies and projectile motion, and was the first to base scientific ideas on the results of experimental observation

The History of Dynamics – Galileo

• Einstein called Galileo the father of modern physics and modern science

“… all knowledge of reality starts from experience and ends in it. Propositions arrived at by purely logical means are completely empty as regards reality. Because Galileo saw this, and particularly because he drummed it into the scientific world, he is the father of modern physics – indeed, of modern science altogether.”

The History of Dynamics – Newton

• In the 1600s, gravity was the only fundamental force what was understood; the electromagnetic force was not well understood and the strong and weak nuclear forces were unknown

• Newton realized that rules for the motion of the universe on a large scale could be used to study other fundamental forces

• Newton predicted that the laws of physics would be able to explain all physical phenomena

The History of Dynamics – Einstein

• Einstein built on Newton’s first law with his special theory of relativity – he considered objects travelling at a constant velocity, close to the speed of light (3.0 x 108 m/s)

• Einstein’s theory of general relativity extended Newton’s second and third laws, explaining accelerating objects and gravity

The History of Dynamics – Hawking

• Hawking continued with the work of the previous three scientists

• He built on Newton’s and Einstein’s work, extending it to such topics as black holes and nature of gravity

• In particular, the idea that black holes can lose mass through something called Hawking radiation

Introduction to Forces

Dynamics • is the study of the cause of motion

Force • is that which changes the motion of an object

or deforms it• a push or a pull• symbol • measured in Newtons, N

Types of Fundamental Forces1. Gravitational

- due to large mass- operates at large distances- attractive force

2. Electric- magnetism, atoms & molecules- operates at short distances- attractive and/or repulsive force

3. Strong Nuclear- protons in nucleus- operates at very small distances

4. Weak Nuclear

- radioactivity

- operates at very small distances

Types of Forces

Force of Gravity – acts on any object in the downward

direction ()

Normal Force – acts upward on any object that is in

contact with another object ()

Applied Force – a force caused by a contact push or pull ()

Force of Friction – acts in the opposite direction to any object that

is in motion ()

Tension – a force from strings, ropes and cables ()

Air Resistance – a force on an object moving through air ()

Force VectorsIn reality, bodies are acted upon by a number of

different forces all at the same time. In order to determine the resulting force on the body, one must find the “net” force or the “unbalanced” force.

Net force has the symbol () and units N

+ + + …

To add vectors together, place the tip of one vector at the tail of the other vector.

The resultant is represented by the vector drawn from the tail of the first vector to the tip of the second vector.

Free Body Diagram• Shows all the forces acting on a body

Ex. A trunk is acted upon by a force of 25 N [N] and 80 N [W]. What is the net force?

Ex. A toy is being fought over by 4 students. Johnny pulls north with a force of 8 N, Billy pulls south with a force of 17 N, Jerry pulls west with a force of 9 N and Andy pulls east with a force of 20 N. What is the net force on the toy?