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1 8th Grade Chapter 2 Notes on Motion Motion: when an object changes its position relative to a reference point. Position: place where something is located Reference Point: a point of interest. An object’s position and reference point describe distance traveled. a. Distance: how far an object has moved, expressed in meters or kilometers. b. Displacement: the distance & direction of an object’s change in position from the starting point. *****distance = displacement IF an object is moving in a straight line***** Finish Line ________________ 80m ________________ 70m ________________ 60m ________________ 50m ________________ 40m ________________ 30m __________________ 20m __________________ 10m Start Line Displacement = 40 m N of starting Distance traveled = 120 meters 2 Speed: the distance an object travels per unit of time. Speed = distance, meters Time, seconds S= d t rate: any change over time. A car is traveling at a constant speed & covers a distance of 750 meters in 25 seconds. What is the car’s speed? Given: D=750 m T = 25 s S=? S=d m t sec. S=d/t; S= 750m/25sec; S=30m/sec Types of speed a. Constant Speed: speed that remains the same-not speeding up or slowing down; cruise control. b. Changing speed: speed that varies and doesn’t stay the same. 3 c. Average Speed: speed of motion when speed is changing. Average speed = total distance total timed. d. Instantaneous Speed: speed at any given point in time; speed read from a speedometer. Graphing Motion 4 Velocity speed AND direction of motion A B A=B speed A opposite B direction so velocity is different Acceleration: the rate of change of velocity; Δ V a. Positive Acceleration speed is increasing b. Negative Acceleration (Deceleration) speed is decreasing Calculating Acceleration Change in velocity = final velocity – initial velocity ΔV=Vf-Vi To calculate acceleration (meters) = Vf-Vi sec² t A=Vf-Vi t 5 * If positive acceleration, A will be a positive number If negative acceleration, A will be a negative number* How are forces and motion related? Force: a push or a pull on an object. Do Objects always move in the same direction of a force? Two types of forces: 1. Balanced forces: forces that are = in size and opposite in direction 6 2. Unbalance forces: forces that are ≠ in size and either opposite or same in direction. 7 8 Net Force: when 2 or more forces act on object at the same time, the forces combine to form the net force. Inertia: the tendency of an object to resist any change on its motion. Bowling ball versus ping pong ball…same inertia??? Bowling ball has a > inertia because the > an object’s mass, the > its inertia. Newton’s First Law of Motion: an object at rest will stay at rest, an object in motion will stay in motion unless it is acted on by an unbalanced force.