Definitions
A point against which direction is measured.
What is the reference point?
Motion is defined as a...
Change in position.
Speed is described in units of...
Distance and time.
When an object is in motion and its velocity changes, we say that the object has experienced...
Acceleration.
What is the average speed of an aircraft that travels 115 miles in 30 minutes? Put your answer in units of miles per hour.
230 mi/h
The distance an object travels plus the direction from the starting point.
What is displacement?
True or False - There are many perfectly stationary objects we can use to judge motion.
False
What is the equation to measure speed?
speed = distance/time
Acceleration units are read...
"meters per second squared" m/s2.
Which of the following quantities could represent a velocity?
A 123 km/s.
B 34 m/min east
C 24 mi/h and slowing
D 15 m west
B 34 m/min east
This word tells you how quickly and in what direction an object is moving in relation to a reference point.
What is velocity?
Motion is always measured relative to something else. What is this called?
Reference point.
Solve. A bus travels 115 miles on the interstate. The bus reaches its destination in 1.5 hours. What is the average speed of the bus?
v = d/t
v = 115/1.5
v = 115/1.5 = 77 mi/h
What is the equation for finding acceleration?
a = vf - vi/t
A child is sledding. He starts at the top of the hill while a velocity of 0, and 3 seconds later he is speeding down the hill at 12 meters per second. What is the child's acceleration?
4 m/s2 down the hill
The time rate of change of an object's velocity.
What is acceleration?
When are displacements used?
When giving directions.
When objects travel in the same direction, their relative speed is the ______________ between their individual speeds.
When objects travel in opposite directions, their relative speed is the ______________ of their individual speeds.
When objects travel in the same direction, their relative speed is the difference between their individual speeds.
When objects travel in opposite directions, their relative speed is the sum of their individual speeds.
True or false - Acceleration can either speed up or slow down an object, depending on its direction.
True
A good runner can keep up a pace of 0.15 miles per minute for quite some time. If a runner starts from rest and settles into a velocity of 0.15 miles per minute south after 3 seconds of running, what is the runner's acceleration over that 3-second interval?
3 mi/min2 south
This word tells you how quickly an object moves in relation to a reference point.
What is speed?
What is a vector quantity?
A physical measurement that contains both magnitude (number) and directional information.
Solve. Two Teslas are self driving down the road while the driver is not paying attention. One Tesla is traveling north at 77 mi/h, while the other is traveling south at 72 mi/h. The Tesla driving north jumps the median and barely misses the Tesla driving south. What is their relative velocity?
v of car 1 - 77 mi/h N v of car 2 - 72 mi/h S
RS = speed of car 1 + speed of car 2
RS = 77 mi/h + 72 mi/h
RS = 149 mi/h
Solve. A cell phone is dropped off a lookout point into the Grand Canyon. It begins with zero initial velocity and it hits the Colorado River 10 seconds later, traveling with a velocity of 15.2 meters per second downward. What is the acceleration?
vi = 0 mps vf = 15.2 mps dn t = 10 s
a = (vf - vi)/t
a = (15.2 mps - 0 mps/2 s
a = 7.6 mps2
What shows acceleration on a speed-time graph?
The slope of the line on a speed-time graph shows the acceleration.