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Phys 1830: Lecture 13

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. Quiz. Radio Arrays can generate spectral line cubes.

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Phys 1830: Lecture 13

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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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