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# Satellites and weightlessness

### Objects in orbit are said to experience weightlessness. They do have a gravitational force acting on them, though! The satellite and all its contents are in free fall, so there is no normal force. This is what leads to the experience of weightlessness.”

• Giancoli Physics, 6th edition

## Newton’s canon: a classic Gedankenexperiment

### A gedankenexperiment is a thought experiment that allows us to learn something new.

Wikipedia article, with animations, of Newton’s cannonball

http://plato.stanford.edu/entries/thought-experiment/

## Newton’s cannon app

### Here are some interactive apps that we can use in class.

http://interactives.ck12.org/simulations/physics/newtons-cannon/app/index.html

http://www.vivaxsolutions.com/physics/newton-cannon.aspx

http://physics.weber.edu/schroeder/software/NewtonsCannon.html

http://waowen.screaming.net/revision/force&motion/ncananim.htm

## Objects in a falling elevator

### When we are accelerating up or down in an elevator, the effective force of gravity we feel is different compared to just standing on the ground.

Giancoli Physics, Chapter 5

## zero-g environment in Earth orbit

### How can we experience weightlessness (briefly) here on Earth? All we have to do is out ourselves in a freefall situation, like this:

Giancoli Physics, Chapter 5, Fig 5-27

## Geosynchronous orbits

### “Because the satellite orbits at the same speed that the Earth is turning, the satellite seems to stay in place over a single longitude, though it may drift north to south,” NASA wrote on its Earth Observatory website…. A satellite in geosynchronous orbit can see one spot of the planet almost all of the time. For Earth observation, this allows the satellite to look at how much a region changes over months or years. The drawback is the satellite is limited to a small parcel of ground; if a natural disaster happens elsewhere, for example, the satellite won’t be able to move there due to fuel requirements.

– What Is a Geosynchronous Orbit? By Elizabeth Howell

https://en.wikipedia.org/wiki/Geosynchronous_orbit#/media/File:Geosynchronous_orbit.gif

http://www.space.com/29222-geosynchronous-orbit.html

Giancoli Physics, Chapter 5

## Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework
HS-PS2-1. Analyze data to support the claim that Newton’s second law of motion is a
mathematical model describing change in motion (the acceleration) of objects when
acted on by a net force.

HS-PS2-10(MA). Use free-body force diagrams, algebraic expressions, and Newton’s laws of motion to predict changes to velocity and acceleration for an object moving in one dimension in various situations

A FRAMEWORK FOR K-12 SCIENCE EDUCATION: Practices, Crosscutting Concepts, and Core Ideas
ESS1.B: EARTH AND THE SOLAR SYSTEM
What are the predictable patterns caused by Earth’s movement in the solar system? Readings on orbits: https://www.nap.edu/read/13165/chapter/11#175

Massachusetts Science and Technology/Engineering Curriculum Framework (2006)
1. Motion and Forces. Central Concept: Newton’s laws of motion and gravitation describe and predict the motion of most objects.
1.7 Describe Newton’s law of universal gravitation in terms of the attraction between two objects, their masses, and the distance between them.
1.8 Describe conceptually the forces involved in circular motion.

SAT Physics Subject Area Test
Gravity, such as the law of gravitation, orbits, and Kepler’s laws

AP Physics Learning Objectives
Essential Knowledge E.3.1
a. The change in the kinetic energy of an object depends on the force exerted on the object and on the displacement of the object during the interval that the force is exerted.

iii. The component of the net force exerted on an object perpendicular to the direction of the displacement of the object can change the direction of the motion of the object without changing the kinetic energy of the object. This should include uniform circular motion and projectile motion.

Learning Objective 5. Orbits of planets and satellites. Students should understand the motion of an object in orbit under the influence of gravitational forces.