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Lecture

# Lecture 2-Chapter 4-Making Sense of the Universe (Motion, Energy, and Gravity)

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University of Toronto St. George

Astronomy & Astrophysics

AST201H1

Stefan Mochnacki

Winter

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Chapter 4 Making Sense of the Universe (Motion, Energy, and Gravity) Describing Motion There are 3 basic terms to describe how an object is moving: 1. Speed tells us how far an object will go in a certain amount of time. N ie, 100kmhr is a speed, which tells us that the car will cover 100 km in an hour. 2. Velocity tells us both the speed and direction of an object. N ie, 100kmhr going due north. 1. Acceleration is when there is a changing velocity in any way, whether in speed or direction or both. N You can often feel the effects of acceleration speeding up in a car would push you back into your seat, and slowing down in a car would pull you forward from the seat, and around a curve would push you away from the direction of your turn. N However, when in constant velocity4:439100O8:.K0110.98 L0,82449K1OLJK943 an airplane. The Acceleration of Gravity N Gravity accelerates all objects by the same amount, regardless of their mass. N However, air resistance can cause a difference in acceleration. o ie, a feather floats gently to the ground, while a rock plummets. N The acceleration of a falling object is called the acceleration of gravity and is equal to 9.8ms^2 downward velocity increases by 9.8ms with each passing second. Momentum and Force N 34-M0.98momentum is its combination of mass and velocity (Momentum = Mass X Velocity). N %K043OZ,94.K,3J0,34-M0.98242039:2L894,55O,force. N The net force (overall force) acting on an object represents the combined effect of all the individual forces put together. o ie, when driving at a constant velocity, the force generated by the engine to turn the wheels precisely offsets the forces of air resistance and road friction; thus, there is no net force on your car. N A change in momentum occurs only when the net force is not zero. N K,3JL3J,34-M0.98242039:220,38.K,3JL3JL98;0O4.L9ZKLO0L982,88-0L3J constant. Thus, the presence of a net force causes an object to accelerate. N In other words, anytime an object accelerates, a net force must be causing the acceleration (causing the feelings of pushes forward, backward, or to the side in a car). Moving in Circles N An ice skater spins in place with zero velocity and hence with zero momentum. Simply, her spin gives her angular momentum (circling momentum or turning momentum). N Any object that is either spinning or moving along a curved path has angular momentum. o ie, Earth has angular momentum due both to its rotation (rotational angular momentum) and to its orbit around the Sun (orbital angular momentum). N The ty5041147.09K,9.,3.K,3J0,34-M0.98,3J:O,7242039:2L8.,OO0,torque (twisting force). www.notesolution.com

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