1. The Science of Motion & Orbits
(Power Point 03)
Image Credit: NASA

2. Student Learning Objectives
Examine the contributions of ancient and modern astronomy to the understanding of gravity and planetary motion.
Describe Motion
Apply Newtonian physics to our solar system
Analyze orbital motion

3. What are the Words used to Describe Motion
Something in motion has a speed, which is how fast the object is moving. (65 mph)
Everything in the universe is in motion.
When we add a direction to the speed, it is called a velocity.

4. Practice
A blue star is traveling through space at 10,000 km/s toward us while a green star is traveling through space at 10,000 km/s away from our solar system.
Both stars have the same speed (True or False)
Both stars have the same velocity (True or False)
Both stars have the same acceleration (True or False)

5. Changes in Motion
When there is a change in velocity, a change in speed or direction, there is an acceleration being caused by some force.
All objects on Earth have the same downward acceleration due to gravity.
9.81 m/s2

6. Practice
If a satellite travelled at a constant speed in a circular orbit, would it have zero acceleration? Explain.
Is the acceleration due to gravity greater on a book or a feather?

8. What are Newton’s Laws of Motion?
Newton’s 1st Law
An object will remain at rest or maintain a constant velocity unless an unbalanced force causes the object’s motion to change. (Inertia)
Inertia is the tendency of an object to maintain its motion.

9. Newton’s 2nd Law of Motion
An unbalanced force acting on a mass gives the mass an acceleration in the same direction as the unbalanced force. (F = ma)

10. Mass vs Weight Mass is the amount of material contained in an object.
Weight is the gravitational force acting on a mass. (W=mg)
Average Man
73 kg
Sun
1.989 x 1030 kg
Earth
5.972 x 1024 kg

11. Practice
Would your mass be different if you were instantly transported to the moon? Explain.
What would your weight be like on Mars where acceleration due to gravity is 3.70 m/s2?

12. Newton’s 3rd Law of Motion
When two objects interact, they create equal and opposite forces on each other. (Action-Reaction)
Same Pull
Opposite Directions
Stock Image

13. NASA's new planet-hunting space telescope, is now in space
Practice
Apply all of Newton’s Laws to a rocket launch.
NASA's new planet-hunting space telescope, is now in space
(April 2018)

14. F = Gm1m2 d2 What is Gravity? Gravity is a property of mass.
Newton’s Universal Law of Gravitation
Every object with mass attracts every other object with mass with a force.
F = Gm1m2 d2

15. Newton’s Mutual Force of Attraction
Both masses pull the same on each other!

16. Inverse Square Law
Force decreases with the square of the distance.

17. Practice
If Earth had twice as much mass, would this change your weight? Would it change your mass?
Is the gravitational force zero in space?

18. Image Credit: wired.com
Weightlessness
The feeling of weightlessness occurs when an object and its reference frame accelerate at the same rate.
Objects fall together.
Image Credit: wired.com

19. What is Einstein’s description of Gravity?
Image Credit: Kurdistan Planetarium

20. Mass & Space Einstein’s Theory of Gravity
Every object with mass creates a curvature of space-time.
Mass does not create a force
Mass changes space
Space alters path of objects and light
More Mass = More Curvature

21. Image Credit: oneminuteastronomer.com

22. Practice
Why doesn’t the Moon fall into the gravity well caused by Earth?
Does an apple cause a curvature of space?

23. Effects of Gravity
Orbits Atmospheres Galaxies Star Formation Shapes of Objects
Orbital Perturbations Synchronous Motion Weight Motion Ocean Tides

24. Gravity & Tides
Credit: NASA

25. Our Changing System
Earth’s rotation is slowing ( seconds/century)
Our Moon is drifting away (3.8 cm/year)
The synchronous orbit of the Moon (same face)
Image Credit: NASA

26. Practice The Sun's tidal affects are weak compared to the Moon. Why?
The astronauts on the space station have no weight. (true or false)
Does the moon have weight? Explain.

27. What is the physics of orbital motion?
Objects move in a straight line, unless an unbalanced force changes the motion.
In circular motion, a centripetal force is causing a change in motion.

28. Falling into Orbit

29. Practice
If the force keeping an object in a circular orbit is removed, what will the new motion of the object be?
What is a geosynchronous orbit?
Does the moon orbit the center of the Earth?
Image Credit: wikipedia

30. Center of Mass
Astronomical objects orbit about the center of mass of the system. (Elliptical Orbits)
Common
Center
Of Gravity

31. What is Conservation of Energy
Kinetic energy is the energy an object has when it is in motion.
Gravitational potential energy is the energy an object has that may fall or travel downward from a height.
Energy cannot be created or destroyed.

32. Conservation of Energy on a Roller Coaster

33. Conservation Of Energy in Space
Elliptical orbits are maintained by conservation of mechanical energy.
Image Credit: Planetary Society India

34. Practice
Where is the motion the greatest in an orbit? What type of energy does a planet have at this location?
Where is the motion the slowest in an orbit? What type of energy does a planet have at this location?
Where in the orbit would a planet have an equal amount of GPE and KE?