1-2 notes – speed, velocity, acceleration. rate a rate measures the change in one quantity in a...

1-2 Notes – 1-2 Notes – Speed, Velocity, AccelerationSpeed, Velocity, Acceleration

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

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

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

SpeedSpeedAn object that moves at a constant An object that moves at a constant speed travels the same distance speed travels the same distance each and every second.each and every second.

This hurdler is moving at a constant speed

of 5 m/s (Every second, she goes 5 m):

SpeedSpeedInstantaneous speed, or the speed of Instantaneous speed, or the speed of an object at a specific instant of an object at a specific instant of time, is especially useful to measure time, is especially useful to measure for objects whose speed changes.for objects whose speed changes.

A car driving in town must slow down and speed up, therefore its speed is not constant.

SpeedSpeed

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

SpeedSpeedThe equation for average speed is:The equation for average speed is:

average speed = average speed = total distancetotal distance total timetotal time

oror

v = v = dd tt

SpeedSpeed

Use the triangle to solve word Use the triangle to solve word problemsproblems

Cover up what’s missing & it tells you Cover up what’s missing & it tells you the math operation to use (multiply the math operation to use (multiply or divide)or divide)

SpeedSpeed1. Genna biked 20 km. in 2 hr. What is 1. Genna biked 20 km. in 2 hr. What is her her speedspeed? ?

10 km/hr

SpeedSpeed2. Jason ran at 5 m/s for 30 s. How 2. Jason ran at 5 m/s for 30 s. How farfar did he run?did he run?

150 m

SpeedSpeed3. Geoff skated at 2 m/s for 200 m. How 3. Geoff skated at 2 m/s for 200 m. How longlong did he skate for? did he skate for?

100 s

SpeedSpeed

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

SpeedSpeed

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

VelocityVelocity

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

VelocityVelocity

Velocity is a vector. It has both a Velocity is a vector. It has both a size (the speed of the object) and a size (the speed of the object) and a direction (the direction the object is direction (the direction the object is moving).moving).

The velocity vector of a ball changes when the direction and speed of the ball change.

Where is its speed increasing?

VelocityVelocity

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

AccelerationAcceleration

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

m/sm/s

ss


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


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


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


When an object changes the When an object changes the direction in which it is moving, its direction in which it is moving, its velocity changes. This means that it velocity changes. This means that it is accelerating.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:Discuss:

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

Discuss:Discuss:Is it possible to accelerate while Is it possible to accelerate while

standing still on the ground?standing still on the ground?

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

Acceleration is the rate of change of ____.

A velocity

B speed

C time

D direction

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


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

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.b

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

SCI 1.c

Velocity has both ____ and ____.

A size; magnitude

B size; speed

C speed; direction

D direction; origin

SCI 1.d

What occurs when an object accelerates?

A It speeds up.

B It slows down.

C It changes direction.

D all of the above

SCI 1.e

1-2 notes – speed, velocity, acceleration. rate a rate measures the change in one quantity in a...

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