The Role of Elementary Physics on the Ordinary – and the Extraordinary!

Based on a Lecture Delivered October 2011

Brad Sottile

Video Discussion Points This mission was STS-122

Goal was to assist in the assembly of the International Space Station

Launch: July 4th, 2006 at 2:37:55 p.m. EDT from Kennedy Space Center, Florida

Landing: July 17th, 2006 at 9:15:49 a.m. EDT at Kennedy Space Center, Florida

Mission Duration: 12 days, 18 hours, 37 minutes and 54 seconds

Sources: Wikipedia and NASA

Video Discussion Points Cont’d The space shuttle Discovery traveled 3.1 million

miles on this mission As referenced in the video, the pilot was a US Navy

Captain by the name of Mark Kelly – he is the wife of Congresswoman Gabrielle Giffords She was wounded in the January 2011 Tucson,

Arizona shooting NASA’s Chief Engineer and Chief Safety Officer

recommended the mission not proceed due to safety concerned but were overruled by their superiors. Was this the right move?

Sources: Wikipedia and NASA

The Space Shuttle and Physics The launch of the space shuttle is just

one (extraordinary) example of the application of physics to the real world!

To begin to adequately describe the world around us, we need to re-examine how we view elementary physics.

Let’s take a step back and time and talk about a rather interesting character by the name of Isaac Newton.

Isaac Newton Born: January 4th, 1643 Died: March 31st, 1727 Was a famous English physicist, mathematician,

astronomer, natural philosopher, alchemist and theologian.

One of his most famous works: Philosophiæ Naturalis Principia Mathematica He wrote the entire book in Latin because he was

paranoid about people stealing his ideas and/or embarrassing him with corrections.

Co-Discoverer of Calculus

Source: Wikipedia

Newton’s Laws First Law (also known as the Law of

Inertia): An object in rest wants to stay in rest while an object in motion tends to stay in motion unless acted on by a force.

Second Law: The Acceleration of an object is parallel and directly proportional to the net force and inversely proportional to the mass of the body.

Third Law: For every action there is an equal and opposite reaction.

Examples and Applications First Law:

Its hard to get out of bed in the morning because your body doesn’t want to move.

Second Law: The second law is famously formulated as

F = m*a Third Law:

If you set a book on a desk, gravity pulls the book down towards the center of the earth; the desk pushes the book up so that there is no net motion experienced by the book.

Equations to Describe Motion Position: Velocity: Acceleration:

denotes initial position, denotes initial velocity

Acceleration is often constant in simple problems

Example Problem Let’s do a very simple example of these

types of physics problems Let’s say we have an apple tree that’s

20 meters tall. If an apple is initially at rest at the top of the tree and falls to the ground, how long will it take for the apple to fall? Ignore any atmospheric effects (e.g. drag) and assume that acceleration due to gravity is constant and is equal to 10 m/s2

Let’s Draw a Picture of This

20 m

We can’t have negative time so disregard the negative root (it is physically impossible!)

Solution

Follow-Up Question: What is the magnitude of the

force acting on the apple if the apple has mass m? F = m*a, where a is the acceleration due

to gravity (the only force on the apple).

Is our result reasonable? Yes!

Think-Pair-Share Activity Think about the following question for a

minute or so then find someone to discuss the solution with!

Given the information in the previous problem, at what speed will the apple hit the ground?

Solution

“Speed” implies that we don’t need to worry about the direction of the movement.

Question: Which way is the apple traveling?

Answer: Towards the ground!

Other Forces There are other forces acting on the space

shuttle than just gravity! Lift can be modeled as

Drag can be modeled as

Where:L = Lift, D = Drag, = Density of Air, = Speed, = Presented Area = Lift Coefficient, = Drag Coefficient

Lift and Drag coefficients are a function of shape and angle of attack – they can be experimentally determined or looked up!