# 1-2 Notes – Speed, Velocity, Acceleration

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1-2 Notes – Speed, Velocity, Acceleration

Rate A rate measures the change in one quantity in a particular length of time. (e.g.) 2 meters per second (e.g.) 5 revolutions per minute (e.g.) 30 belches per minute

Speed Speed is the rate of change of position over a period of time.

Speed Speed, velocity, and acceleration describe how an object’s position and motion change through time.

Speed An object that moves at a constant speed travels the same distance each and every second. This hurdler is moving at a constant speed of 5 m/s (Every second, she goes 5 m):

Speed Instantaneous speed, or the speed of an object at a specific instant of time, is especially useful to measure for objects whose speed changes. A car driving in town must slow down and speed up, therefore its speed is not constant.

Speed An object’s average speed is its total distance traveled divided by the total time it traveled.

average speed = total distance
The equation for average speed is: average speed = total distance total time or v = d t

Speed Use the triangle to solve word problems
Cover up what’s missing & it tells you the math operation to use (multiply or divide)

Speed 1. Genna biked 20 km. in 2 hr. What is her speed? 10 km/hr

Speed 2. Jason ran at 5 m/s for 30 s. How far did he run? 150 m

Speed 3. Geoff skated at 2 m/s for 200 m. How long did he skate for?

Speed If you know any two quantities in the average speed equation, you can use the equation to calculate the third.

Speed The unit for speed is a distance unit (meters) divided by a time unit (seconds). The SI unit for speed is m/s.

Velocity Velocity is a measurement of both the speed and direction of motion of an object.

Velocity Velocity is a vector. It has both a size (the speed of the object) and a direction (the direction the object is moving). The velocity vector of a ball changes when the direction and speed of the ball change. Where is its speed increasing?

Velocity Speed is different from velocity because speed does not include the direction in which the object is moving.

Acceleration Acceleration, another vector, is the rate at which velocity changes over time. m/s s

Acceleration When an object speeds up or slows down, its velocity changes, meaning that it is accelerating.

Acceleration When an object speeds up, the direction of its acceleration is the same as the direction of its motion.

Acceleration When an object slows down, its acceleration is in the opposite direction from the direction of its motion.

Acceleration When an object changes the direction in which it is moving, its velocity changes. This means that it is accelerating. The horses on the carousel are constantly accelerating and changing direction, so they are constantly changing velocity even though their speed remains constant.

Discuss: Is it possible to accelerate while standing still on the ground?

Discuss: Is it possible to accelerate while standing still on the ground? Yes! It all depends on your point of reference. Even if you are standing still with respect to the ground beneath you, you are moving because Earth itself is moving. It rotates around its axis, and revolves around the Sun.

Acceleration is the rate of change of ____. A velocity B speed C time
1.2 Speed, Velocity, and Acceleration Acceleration is the rate of change of ____. A velocity B speed C time D direction

A car stopping at a red light is an example of a(n) ____.
1.2 Speed, Velocity, and Acceleration A car stopping at a red light is an example of a(n) ____. A displacement B acceleration C direction D velocity

1.2 Speed, Velocity, and Acceleration
It takes a runner 50 s to run a distance of 150 m. What is the runner’s average speed? A 0.3 m/s B 3 m/s C 100 m/s D 50 m/s

A runner traveling at 5 m/s will cover what distance in 3 min?
A 900 m B 90 m C 9 m D none of the above

If a car travels 10 km in 5 min, stops for 2 min, and then travels 4 km in 3 min, what is the average speed of the car? A 14 km/h B 14 km/min C 1.4 km/min D 1.4 km/h

Cars on an oval race track are accelerating because ____.
A they are changing direction B their displacement is zero C all of the above D none of the above

If an object increases its speed, then it is ____.
A changing velocity B changing direction C changing the reference direction D none of the above

SCI 1.b Which of the following is the rate of change in distance divided by time? A vector B displacement C instantaneous speed D average speed

SCI 1.c If a car travels 45 km in half an hour, what is the average speed of the car? A 45 km/h B 45 km/min C 90 km/h D 90 m/s

Velocity has both ____ and ____. A size; magnitude B size; speed
SCI 1.d Velocity has both ____ and ____. A size; magnitude B size; speed C speed; direction D direction; origin

What occurs when an object accelerates? A It speeds up.
SCI 1.e What occurs when an object accelerates? A It speeds up. B It slows down. C It changes direction. D all of the above