Unit II – Speed, Motion, Velocity and Acceleration Physical Science Unit II – Speed, Motion, Velocity and Acceleration

Describing Motion

Motion For Motion to occur, the position of an object must change Its Displacement is the difference in position

Displacement Displacement (or change in position) is measured in the SI unit meter m. What is the displacement of a runner that jogs 100m and back? What is the displacement of a runner that jogs 100m in one direction?

Solving Motion Problems Use scientific formulas to solve for variables. Ex: what is the speed of a rabbit that travels 1.3 km in 30 min?

Speed Speed is equal to change (Δ) in distance divided by time. Abbreviated equation s = d t Common units for speed: mph (miles per hour) m/sec (meters per second) km/hr (kilometers per hour)

Calculating Speed What is the speed of a car that travels 80 km in 2 hours?

Speed = distance s = d time t Speed = 80 km 2 hours Speed = 40 km/hr

Solving motion problems Remember to set up problem to solve for x Remember all variables in a formula have a unit of measurement Change the formula around to solve fore the variable that you want. s=d/t d=st t=d/s

Average Speed and Instantaneous Speed Average speed is total distance divided by total time. ex: If you travel 50 meters in 10 sec, your average speed is 5 m/sec Instantaneous speed occurs while an object is in motion. ex: think of your speedometer on your car

Graphing motion Place time on the x – axis Place distance on the y-axis Label units Connect points to show a trend The slope of the line is your speed!

Velocity What is velocity? Speed with a direction EX: 12 m/sec west 52 mph down 8000 m/sec forward A unit of speed is assumed to be velocity if the direction of motion is obvious

Solving velocity problems What is the velocity of a water balloon that falls 16m in 3.2 sec? S=d/t S = 16/3.2 Velocity = 1.88 m/s down