Important Vocabulary Speed vs Velocity Acceleration Graphs of Motion Momentum
Important Vocabulary Position-location of an object Distance-how far an object has traveled, regardless of direction Displacement-change in position in relation to starting point, including direction Speed-distance per unit time Velocity-displacement per unit time Acceleration-change in velocity per unit time Momentum-mass times velocity of a moving object
The position of any object must be given with respect to some reference point. Movement is said to have occurred when the position of an object has changed from where it was when it started.
A displacement of -3.5 m implies movement of 3.5 m in the negative direction. (or left) A displacement of +3.5 m implies movement of 3.5 m in the positive direction. (or right) + In motion, the displacement direction is often given as positive, +, or negative, -. - + -
I traveled to my house about 25 miles away and then traveled back. My total distance traveled was 50 miles, but what was my displacement? My displacement was zero, because I ended up back where I started.
Speed Speed is a measure of the distance traveled per unit time. Speed is always positive Standard units for speed are m/s The formula for calculating speed is: Speed = Distance Time Clue words for speed: how fast, m/s, distance per time Units for speed: m/s
Velocity Velocity is the distance per unit time, also The difference between speed and velocity is that velocity takes into account the direction Velocity can be + or Standard units for velocity are m/s Velocity includes which direction you are traveling! Formula for calculating velocity: Velocity = Displacement Time
Velocity is speed with direction. The sign of the velocity indicates the direction of movement. A positive sign indicates movement in the positive direction.(or right) A negative sign indicates movement in the negative direction.(or left) + -
Average speed and average velocity are generally not equivalent because total distance and total displacement are generally not the same. When would they have the same magnitudes?
Speed and Velocity Average Time = 1 min 18 sec averagespeed speed total distance time Start Finish = 500 m 500 78 average velocity m 6.4 s 0 m 0 78 s m s m s Average velocity v total displacement time s t Is it possible to move with constant speed but not constant velocity? Yes. (Cruising at 55 mph around a corner changing direction = changing velocity) Is it possible to move with constant velocity but not constant speed? No. (A change in speed would cause a change in velocity.)
Acceleration Acceleration is the change in velocity (not speed) per unit time Units for acceleration are: m/s 2 Formula for calculating acceleration is: Acceleration = v t or Final Velocity Beginning Velocity Change in Time Clue words: change in velocity, m/s 2
Acceleration change in velocity Average acceleration time v a t Positive acceleration means increasing velocity accelerating or speeding up Negative acceleration means decreasing velocity or decelerating or slowing down
Graphs of Motion There are three types of motion graphs that you need to be familiar with and understand: 1. Position vs time 2. Velocity vs time
General Info about Graphs All graphs must have a title at the top of the graph All axes must be labeled to be complete Axis label includes both the quantity and the units for example, a y axis complete label: position, (m) Graphs turned in for class should also include the data table For lab data, you need to draw a best fit line unless otherwise instructed on the individual lab. A best fit line doesn t necessarily go through all the points on the graph, but is the line that goes through the majority of points.
Position vs Time x axis is the time the object has been in motion y axis is the position of the object in motion change in position is the distance traveled the slope of the line is the velocity of the object. Slope is: slope rise run y x position time Remember that velocity is: velocity displaceme time nt position time
Velocity vs Time Graphs x axis is the time the object has been in motion y axis is the velocity of the object the slope of the line is the acceleration of the object. Slope is: slope rise run y x remember that acceleration is: velocity time a velocity time v t
Which had the greatest velocity? a. Distance 3m time 1s=3m/s b. Distance 2m time 2s= 1m/s c. Distance 1m time 3s=0.33m/s
Momentum Momentum is the mass of an object times it s velocity Momentum s formula: momentum p mv Velocity mass Momentum gives us a way to evaluate how mass interacts with velocity Law of conservation of momentum says that the total momentum of a system before and after a collision is the same
Both mass and velocity must be considered when changing an object s motion. More force is needed to stop a train moving than to stop a car, even though they both have the same speed. More force is needed to stop a baseball thrown at 85mph than to stop a baseball thrown at 35 mph.
Momentum Momentum has direction The stopping distance of an object like a car is related to its momentum. When two objects collide they transfer their momentums to each other--momentum lost by one object is gained by another when they collide.