Chapter 2 Motion and Speed

Section 1 Describing 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.