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summary Phys 1830: Lecture 13 Recall column 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 Recall column summary Radio Arrays can generate spectral line cubes. summary Recall column Saw 3D cube with x+y spatial position and z axes velocity. Velocity field of NGC 3556 using HI 21 cm emission. • 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. Example of another velocity field: The Vela Cloud summary Recall column • The galaxies rotation can be seen on right. • Note that the cloud doesn’t have any distinct flows. Constructing Colour Images: The W4 Chimney Region in the Milky Way summary Recall column • 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. Another example of velocity field: English & Taylorsummary Recall column • 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. Seeing Gravity: Laws of Motion Recall column summary Motion summary Recall column Angular Momentum • Defined as the tendency of a body to keep spinning (i.e. rotating) or moving in a circle (i.e. revolving). Motion summary Recall column • 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. 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. Newton’s First Law: The law of inertia Recall column summary • Demo with cart – ignoring friction: 1) Cart at rest needs a force to make it move. 2) Cart in motion needs a force to make it stop. Newton’s First Law: The law of inertia Recall column summary • 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. Newton’s Second Law: Acceleration summary Recall column 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 Question: Recall column summary • Demo: – Ball on a string. The Force is the tension on the string. – If there is no string what happens? a) The ball drops instantly straight to the ground. b) The ball continues in the circle for a while. c) The ball travels in a straight line in the direction it was already moving. Newton’s Second Law: Acceleration summary Recall column 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 Newton’s Second Law: Acceleration summary Recall column • 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. Newton’s Third Law: Equal and Opposite Reaction summary Recall column • When object A exerts a force on object B, object B exerts an equal and opposite force on object A. Demo: a)Container with water and coin to drop in it. b)2 carts push equally on each other. c)Balloon on straw on string. Balloon goes in opposite direction to airflow. a) Elastic collapse causes a force that pushes air out of balloon nozzle. b) Air pushes back with equal force on elastic causes balloon to move. summary Review Questions: Recall column • With your neighbours, see if you can list Newton’s 3 laws of motion. (Hint: use a word or a few to describe each.) summary Motion: Recall column • Angular Momentum • Newton’s Laws 1. Inertia 2. Acceleration 3. Equal and opposite reaction summary Review Question: Recall column 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. a) Larger b) Smaller c) Same