CH. 2 Notes Abbreviated

Distance vs. Displacement Distance – the length an object travels (meters) Displacement – straight line path between two points. (must have a direction)

Speed Speed is the distance an object travels per unit time. 55 mph or 10 m/s Metric (SI) unit is meters/second Calculating speed:

Distance-Time graphs Distance – Always y-axis Time – Always x-axis Slope of the line = speed Δy / Δx = slope Horizontal line = no motion Steep line = greater speed

Velocity Velocity is speed with a direction Ex. 55 mph North Because velocity depends on direction as well as speed, the velocity of an object can change even if the speed of the object remains constant. The speed of this car might be constant, but its velocity is not constant because the direction of motion is always changing.

Acceleration Acceleration is the rate of change of velocity. When the velocity of an object changes, the object is accelerating. A change in velocity can be either a change in how fast something is moving, or a change in the direction it is moving. Acceleration occurs when an object changes its speed, its direction, or both.

Speeding Up and Slowing Down If the acceleration is in the same direction as the velocity, the speed increases. Acceleration is positive. If the speed decreases, the acceleration is in the opposite direction from the velocity, and the acceleration is negative.

Changing Direction Any time a moving object changes direction, its velocity changes and it is accelerating.

Calculating acceleration

Practice A runner covers the last straight stretch of a race in 4 s. During that time, he speeds up from 5 m/s to 9 m/s. What is the runner’s acceleration in this part of the race? a= 9m/s – 5 m/s 4s a= 1m/s/s or 1 m/s2

speed-time graphs graph shows acceleration positive slope (going up) = increasing acceleration negative slope (going down) = decreasing acceleration speed @ 0 = no motion horizontal line = constant speed (velocity)