Transcript Chapter 2
Chapter 2 Motion and Speed Section 1 Describing Motion • Motion – Distance- how far an object has moved – Displacement- DISTANCE AND DIRECTION of an object’s change of position from a starting point How do distance and displacement differ? Describing Motion-cont. • Speed – – – – – Rate- any change over time Speed=distance/time constant speed doesn’t change over time objects usually have a changing speed instantaneous speed-speed at any given point in time What are two examples of motion in which the instantaneous speed changes? Describing Motion-cont. • A distance-time graph displays motion of an object over time. – Plot distance an a vertical axis – Plot time on a horizontal What was the average speed of each swimmer over the 30-min period? Describing Motion-cont. • Velocity-SPEED and DIRECTION of an object’s motion • Motion of Earth’s crust—so slow we don’t notice How are velocity and speed different? How do the continents drift? Section 2 Acceleration • Acceleration-change in velocity’s rate – Positive acceleration-speed is___________ – Negative acceleration-speed is ___________ – When an object changes speed or direction, it is accelerating Acceleration-cont. • Calculating acceleration – acceleration=change in velocity/time – change in velocity=final velocity-initial velocity – unit for acceleration=meters per second squared – positive acceleration= +# with a + slope on a velocity-time graph – negative acceleration= -# with a –slope on a velocity-time graph Acceleration-cont. • Amusement park acceleration-roller coasters – Changes in SPEED cause acceleration. – Changes in DIRECTION cause acceleration. What material are roller coasters with the steepest hills made from? Section 3 Motion and Forces • Force- a push or pull that one body applies to another – A force can cause an object’s ______ to change, – When two or more forces combine at the same time, they create a net force. – balanced forces are equal in size and opposite in direction – unbalanced forces are unequal in size and / or are not in the same direction Motion and Forces-cont. • Inertia and Mass – Inertia- an object’s resistance to any change in motion. – Objects with greater _____ have greater inertia. – Newton’s first law of motion- an object’s moving at a constant velocity keeps moving at that velocity unless a net force acts on it; an object at rest will stay at rest unless a net force acts on it. Motion and Forces-cont. • Auto crashes-the law of _________ at work. – A passenger not wearing a seat belt keeps moving ________ at the car’s speed even after the car stops. – A passenger wearing a seat belt slows down as the car slows down and stops.