Linear Motion Chapter 2 Speed Velocity and Acceleration

Linear Motion Chapter 2 Speed, Velocity, and Acceleration

2. 1 Motion is Relative n Everything moves, even things that appear to be at rest, relative to the sun and stars. n Unless stated otherwise, when the speeds of things in the environment is discussed, it is with respect to the surface of the Earth.

2. 2 Speed n n Speed is a measure of how fast something is moving, or the rate at which distance is covered per unit of time. Any combination of units for distance and time that are useful and convenient are legitimate for describing speed. miles per hour (mi/h) n kilometers per hour (km/h) n meters per second (m/s) n

2. 2 Speed n n Instantaneous speed is speed at any instant of time. Average speed is path distance divided by time interval. n average speed = total distance total time

2. 3 Velocity n n Velocity is speed together with the direction of motion. Speed is a description of how fast an object moves. Velocity is how fast and in what direction it moves. Constant velocity requires both constant speed and constant direction.

2. 3 Velocity n n Changing velocity occurs if either the speed or the direction (or both) is changing. In a car there are three controls that are used to change the velocity. The gas pedal is used to maintain or increase the speed. n The brake is used to decrease the speed. n The steering wheel is used to change the direction. n

2. 4 Acceleration n The rate at which the velocity is changing is called acceleration. n n n acceleration = change of velocity time interval Negative acceleration is called deceleration. Acceleration also applies to changes in direction as well as speed.

2. 4 Acceleration n Speed and velocity are measured in units of distance per time. The units for acceleration are those of speed per time. Some examples of units for acceleration include: miles per hour-second (mi/h·s) n kilometers per hour-second (km/h·s) n meters per second-second (m/s 2) n