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Exploring Motion and Laws of Gravity in Astronomy

Discover the dynamics of motion, angular momentum, and Newton's laws in astronomy, including insights on radio arrays, velocity fields, and gravity. Unveil the mysteries of celestial mechanics in this engaging lecture.

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Exploring Motion and Laws of Gravity in Astronomy

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  1. Phys 1830: Lecture 13 The Vela Cloud J. English Coming up: Tides General Relativity • Previous Classes: • Workshop on image-making • Doppler Shift • Velocity Fields • This Class • Motion • Angular Momentum • Newton’s Laws • Gravity

  2. Quiz

  3. Radio Arrays can generate spectral line cubes. Velocity field of NGC 3556 using HI 21 cm emission. Saw 3D cube with x+y spatial position and z axes  velocity. • The 21 cm line is particularly useful since radio arrays make images per channel. Each channel represents a narrow velocity range. • Professional astronomy tools like the Karma suite help astronomers interpret these 3D cubes.

  4. Example of another velocity field: The Vela Cloud • The galaxies rotation can be seen on right. • Note that the cloud doesn’t have any distinct flows.

  5. Constructing Colour Images: The W4 Chimney Region in the Milky Way • Radio Continuum data is coloured to distinguish thermal plasma and synchrotron emission. • HI radio data is coloured to show the motion in the gas. Blue is assigned to blueshifted gas  rotation of the Milky Way.

  6. English & Taylor Another example of velocity field: • H I gas in our Milky Way which could effect our understanding of the Cosmic Microwave Background Radiation by absorbing microwaves. • The animation shows that this gas doesn’t have signatures of flow or rotation. Its motion is turbulent.

  7. Seeing Gravity: Laws of Motion

  8. Motion Angular Momentum • Defined as the tendency of a body to keep spinning (i.e. rotating) or moving in a circle (i.e. revolving).

  9. Motion • Must be conserved within a system. • person on spinning chair brings in their arms • Bicycle wheel  transfer of angular momentum • Flashlight shows how an object can beam light when spinning.

  10. Newton’s Laws Newton’s First Law: The law of inertia. An object at rest will remain at rest, and an object moving in a straight line at constant speed will not change its motion, unless an external force acts on it.

  11. Newton’s First Law: The law of inertia • Demo with cart – ignoring friction: • Cart at rest needs a force to make it move. • Cart in motion needs a force to make it stop.

  12. Newton’s First Law: The law of inertia • Inertia is the tendency of an object to keep moving at the same speed and in the same direction. • Definitions: • Velocity has • Amplitude (speed) • Direction • Acceleration • Change in amplitude or direction.

  13. Newton’s Second Law: Acceleration F == force m == mass a == acceleration • When a force is exerted on an object, its acceleration is inversely proportional to its mass: • a = F/m

  14. Question: • Demo: • Ball on a string. The Force is the tension on the string. • If there is no string what happens? • The ball drops instantly straight to the ground. • The ball continues in the circle for a while. • The ball travels in a straight line in the direction it was already moving.

  15. Newton’s Second Law: Acceleration F == force m == mass a == acceleration • When a force is exerted on an object, its acceleration is inversely proportional to its mass: • a = F/m

  16. Newton’s Second Law: Acceleration • Demo: • Cart: starting from rest , what do we do to change its speed. - Constant F  constant a. • Greater F  greater a. • increase mass  decrease a. • decrease mass  increase a.

  17. Newton’s Third Law: Equal and Opposite Reaction • Demo: • Container with water and coin to drop in it. • 2 carts push equally on each other. • Balloon on straw on string. Balloon goes in opposite direction to airflow. • Elastic collapse causes a force that pushes air out of balloon nozzle. • Air pushes back with equal force on elastic causes balloon to move. • When object A exerts a force on object B, object B exerts an equal and opposite force on object A.

  18. Review Questions: • With your neighbours, see if you can list Newton’s 3 laws of motion. (Hint: use a word or a few to describe each.)

  19. Motion: • Angular Momentum • Newton’s Laws • Inertia • Acceleration • Equal and opposite reaction

  20. Review Question: Fill in the blank: • According to Newton's second law, when the same force acts on two bodies, the body with the larger mass will have the ________ acceleration. • Larger • Smaller • Same

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