Science 20 F

Physics Outcome 3: AccelerationA – Level understanding (everyone needs to do)

Explain what acceleration is Explain what it feels like to be accelerating in a vehicle Give examples illustrating that people can’t “feel” speed but they can

“feel” acceleration Calculate an acceleration when you’re given the initial velocity, the

final velocity and the time it took to change the velocity Recognize the difference between an average speed problem and an

acceleration problem and solve either using the appropriate method

B – Level understanding (should do if you want to do further physics studies next year)

Explain similarities and differences between acceleration and velocity Calculate initial or final velocities when the acceleration and time of

accelerating are known Explain conceptually WHY the calculations in B – Level make sense

C – Level understanding (Would be nice to do if you want to show mastery – level understanding of the outcome)

Calculate the time needed to change speed when the acceleration and initial and final speeds are known

Communicate calculations in a well – organized fashion utilizing proper math conventions

Explain conceptually WHY the calculations in C – Level make sense. Complete a lab that uses ticker tape analysis to measure the acceleration of an object.

Up to

60%

Up to

80%

Up to

100%

[Type here]

Activity 1: What is AccelerationPart 1: Exploring Background Knowledge

What do you feel when you’re moving really fast but NOT accelerating?

What do YOU mean if you say an object is accelerating?

When you’re IN a vehicle, how do you recognize that it is accelerating?

2

Our bodies don’t feel speed; we feel ONLY acceleration!

Large acceleration Small Acceleration

…what do you see?

… what do you feel?

[Type here]

What exactly is acceleration then?

Conceptual Questions:

1. Give an example of where YOU have been travelling very fast but not accelerating so you didn’t really feel like you were moving.

2. Think about being in an elevator in the tallest building you have ever been in.a. When does it for sure feel like you’re moving? Why?

b. When might it feel like you are NOT moving even though you are?

3

and even changing direction!.slowing down,

In physics…… acceleration includes speeding up,

Definition Definition in symbols Units

[Type here]

Part 2: Measuring acceleration using YouTube

Watch the videos your teacher shows you. Use the stop watch provided to time how long each change in speed takes to happen. Then, with your table partner, determine the acceleration of:

1. The Mercedes- Benz S500 as it accelerates from 0 – 120 km/hr.

2. The Audi S4 B6 as it accelerates from

a. 100 – 160 km/hr

b. 200 – 240 km/hr

4

Change in velocityHow much time it took

Change in velocityHow much time it took

Change in velocityHow much time it took

Write a description of what you would have felt if you had been riding in the Audi S4 – B6.

[Type here]

Discussion: Acceleration is NOT speedWhich has the greater speed….

Which has the greater acceleration…

5

Top Speed

km/hr0

Top Speed

km/hr0

The space shuttle?The fastest bullet in the world?Winchester .223 Super Short Magnum

km/hr0 0

Acceleration is NOT speed. Write what the MAIN difference between them is.

km/hr

hrkm /

sm /

[Type here]

Sample Acceleration Problems

1. Mrs. Brown is driving to 7-Eleven at a speed of 30 km/hr. She notices someone walking down the street with a Slurpee™ and decides she needs a Slurpee™ NOW! She changes speed to

95 km/hr in just 3.0 seconds. Calculate Mrs. Brown’s acceleration in km /hrs .

2. A mouse is scurrying along with a speed of 3.0 m/s when it realizes it is being followed by a cat. For obvious reasons, it accelerates to a speed of 12 m/s over the short time of 2.0

seconds. Calculate the mouse’s acceleration in m /ss .

6

Acceleration tells you how fast your velocity is changing (in grade 10, how fast the reading on your speedometer is changing).

So its units are things like:

km /hrs

or m /ss

Acceleration is “how much your velocity changed divided by how long it took.”

o In symbols we write: a=∆v∆ t

o To find the change in velocity, we sometimes have to subtract the speed we ended up at minus the speed we started at. Drawing speedometer pictures helps!

A – Level Instruction: Calculating accelerations

hrkm /

hrkm /

[Type here]

3. Mrs. B is driving to school at a speed of 100 km/hr. Suddenly, she encounters a great big mountain of Jell-o™ on the road (Yikes). It takes her 5 seconds to pass through the

Jell-o™ and the Jell-o™ slows his car at a rate of 8.0

km/hrs , how fast is she traveling as

she leaves the Jell-o™ mountain?

4. Mrs. B’s scooter can accelerate at a rate of 4.0

km /hrs . If she is initially driving in town with a

speed of 50 km/hr, how long does it take Mrs. B. to reach her cruising speed of 96 km/hr once she hits the highway?

7

C – Level instruction: Calculating times

hrkm /

sm /

[Type here]

Assignment

1. An un-named Grade 10 science student is cruising the Shaftesbury strip (ie. circling in the parking lot in front of Shaftesbury) at a cautious speed of 30 km/hr when he spots Mrs. B. leaving the school. The student floors it reaching a speed of 90 km/hr in just 5.0 seconds just before running over Mrs. B. (that’ll teach her for giving homework in the last 10 minutes of class). Calculate the acceleration of the student’s car.

2. A rabbit is hopping along with a speed of 3.0 m/s when it smells a big bowl of ice cream ahead on the path (the whole rabbits and carrots thing is really a myth – they

actually prefer ice cream). The rabbit accelerates at a rate of 0.40 m /ss

for 8.0 seconds. What is the rabbit’s final speed?

8

A – Level

B – Level

hrkm /

[Type here]

3. A car can slow down at a rate of – 8 .0

km /hrs . How long does it take the car to slow

from a speed of 90 km/hr to a speed of 50 km/hr?

4. What does acceleration really tell us? What will its units look like.

5. Suppose your car was moving at 20 km/hr when you started accelerating at a rate of

12 km/hrs . Draw pictures of your speedometer at the times below to show you

understand what this really means.

9

t = 0 sec t = 1 sec t = 2 sec t = 3 sec

C – Level

A – Level

A – Level

hrkm /

sm /

[Type here]

6. A car is driving with a speed of 120 km/hr. The driver lightly applies the brakes,

slowing down at a rate of 8

kmh

s for 3.5 seconds. What speed does the car end up travelling at?

7. A cheetah walking at a speed of 3 m/s sees a wild ice-cream cone running through the grass and accelerates to catch it (just like rabbits, cheetah’s love ice-cream!). If the cheetah reaches a speed of 25 m/s after a time of just 3.2 seconds, what was the cheetah’s average acceleration?

10

B – Level

A – Level

[Type here]

Extra Practice:A – Level

1. A car slows from a speed of 120 km/hr to a speed of 95 km/hr during a time of 2 seconds. What is the car’s average acceleration?

2. An excited physics student rushes to the front of the room to be the first person to get to ride the hovercraft. The student accelerates from rest to a speed of 12 m/s in three seconds. What was the student’s average acceleration?

3. A car travelling at 50 km/hr through town accelerates to a speed of 110 km/hr as it reaches the highway speed zone. If it took 5 seconds to speed up, what was the car’s average acceleration?

4. A kid on a skateboard slows from a speed of 15 m/s to a speed of 7.0 m/s over a time of 3 seconds. What was the skateboard’s average acceleration?

B – Level

5. A car has a speed of 55 km/hr and accelerates at a rate of 5 km /hrs for 12 seconds.

What is the car’s final speed?

6. A car ends up with a speed of 50 km/hr after slowing at a rate of 15 km /hrs for 4

seconds. What was the car’s initial speed?

7. If a dog with an initial speed 4 m/s accelerates at a rate of 8 m /ss for 1.5 seconds, what

is the dog’s final speed?8. Explain why it makes sense that “ at=∆v” and that to get v f you add vi+∆v

C – Level

9. A car has an acceleration of 8 km /hrs . How long does it take the car to change

speeds from 40 km/hr to 100 km/hr?

10. A car slows at a rate of 12 km /hrs . How long does it take a car traveling at

110 km/hr to slow to a speed of 50 km/hr?11. A hockey puck accelerates from a speed of 3 m/s to a speed of 35 m/s

during a slap shot. If the acceleration of the puck is 45 m /ss , for how long is the

stick in contact with the puck during the slap shot?12. Explain why it makes sense that to find the time that something

accelerated for, you divide how much the velocity changed by the acceleration.

11

[Type here]

t=∆va

12

[Type here]

ANSWERS:

Practice Acceleration Problems

1. 12 km /hrs

2. 6.2ms

3. 5 s

6. 92 kmhr

7. 6.9 m /ss

Extra Practice

1. −12.5 km /hrs

2. 4 m / ss

3. 12 km /hrs

4. −2.7 m /ss

5. 115km /hr

6. 110km /hr

7. 16m /s

9. 7.5 s

10. 5 s

11. 0.71 s

13

[Type here]

14

[Type here]

Mixing it UpIn this assignment, you get to practice recognizing the difference between speed – time problems and acceleration – time word problems.

Field Trip to the Amusement Park

1. Abby “I don’t find swiss chard very flavourful – in fact I think its rather Bland-chard” runs toward the entrance gate so that she can be the first inside (she wants first pick of the horses on the merry-go-round). If Abby sprints the 200 m from the bus to the gate in a respectable 20 seconds, what was her average speed?

Does this mean Ms. Bland-chard was running at that speed through her whole sprint? Explain.

2. Jenna “I started a towing service with a theme – all the drivers wear old fashion ladies hats. Its called ‘Jenna’s Bonnet Tow” is driving a bumper car. She spots Mr. Kitching a short distance away (with his back to her). Seizing the opportunity, Ms. Bonnet - tow accelerates her car from 4 km/hr to a colliding speed of 18 km/hr in just 3 seconds. Calculate the acceleration of Jenna’s car.

b) After the collision Jenna’s car is moving forward at just 7 km/hr. If the collision took 0.8 seconds, calculate the acceleration of Ms.

Bonnet-tow's car during the collision.

3. Alexyss “my brother got me a crappy birthday present but a really nice card, so, always finding the positive in situations, I just said, ‘Nice Card-man!’” runs at a speed of 13 m/s as she hurries to the Ferris wheel. If it takes her 8.6 seconds to reach the Ferris wheel, how far was Ms. Card-man from it when she started to run?

15

A - Level

A - Level

B - Level

B - Level

Mr. Rogers planned a trip to the amusement park for his Science 20S class. Although budgetary constraints prevent us from actually taking you there, money does allow the printing of this pamphlet summarizing the good times we would have had if we had gone. Names have been changed to protect the identity of individuals.

[Type here]

4. Cole “I want to start a fast food restaurant that sells only poached eggs at a drive through. I’ll call it Poach- n’-go” is riding the “Drop of Doom”. During the ride, the cart travels a distance of 200m at an average speed of 35 m/s. How long does Mr. Poach-n-go’s trip take?

5. Jaxon, “I invented a weapon that freezes people when I shoot it at them – I call it my Brrrr - gun' ” is riding the roller coaster. The coaster passes over the top of one peak with a speed of 20 km/hr. By the time it reaches the bottom of the next dip 4 seconds later, it is traveling at a speed of 110 km/hr. What was the average acceleration of the cart during this time?

b) Mr. Brrrr - gun tops the next peak with a speed of 37 km/hr. If he accelerates for the next 5 seconds at a rate of 12 km/hr/second, how fast does he end up going?

6. Dylan “My buddy Kurt likes to fly around on a broom, so, even though I know it is not politically correct, I call him Kurt – the witch” is on his way to buy some cotton candy. He notices Mr. Kitching heading to the same confectionary stand to buy the last bag. Yikes! Dylan quickly changes speed from 3 m/s to 12 m/s in a mere 2 seconds. Calculate Mr. Kurt-the-witch's acceleration.

7. Harmony “I like kale in salads, smoothies, sandwiches, chips, ice cream – you could say I’m a true Kaler” decides to bungee jump off a crane at the amusement park. Starting from rest (speed = 0) she reaches a speed of17.2 km/hr in just 1.75 seconds. What was her acceleration?

8. Katelyn “I love making scarfs, especially when people around me are dancing and listening to loud music so I can hardly wait until I turn 18 so I can Bar-knit” rides the Merry-Go Round. The horses travel in a circular path with a radius of 3 metres and take 7 seconds to complete one full revolution. Find Ms. Bar-knoit’s speed. Hint: Calculate the distance the horses travel as they

go around the circle! (C = 2r)

16

B - Level

A - Level

B - Level

A - Level

B - Level

C - Level

[Type here]

9. Andrew “my mom kept sending me annoying texts telling me I should be nicer to Mr. Rogers, so I finally just Blocked-her” is heading back to the bus to return to the school. He walks at 2 km/hr but then accelerates to 11 km/hr when he notices someone else trying to take the seat at the back beside the bathroom (he had eaten one too many corn dogs). If he sped up over a time of 1.5 seconds, what was Mr. Blocked-her’s acceleration?

17

A - Level

[Type here]

ANSWERS: Fieldtrip to the Amusement Park

1. 10m /s

2. a) 4.7 km /hrs b) 13.8 km /hr

s

3. 112m

4. 5.7 s

5. a) 22.5 km /hrs b) 97 km/hr

6. 4.5 m /ss

7. 9.8 km /hrs

8. 2.7 m/s

9. 6 km /hrs

18

[Type here]

C – Level Lab: Motion down a RampObjective: To measure the acceleration of a toy car rolling down a ramp.

Specifically, • to create a position – time graph of the motion• to measure two velocities of the car at different times• to determine the acceleration of the object

Apparatus:

Ticker Timer Ticker tape 2 C-clamps Masking tape Toy car Ramp Books Metre stick

Procedure:

1. Set up the apparatus as shown. The ticker tape must go under both staples and under the purple carbon paper disk. Attach the ticker tape to the car with a small piece of masking tape.

2. One member of the group holds the car motionless at the top of the ramp. 3. Another member of the group turns on the ticker timer. A third spins the carbon disk.4. Once the timer is started, the car is released. Do not push the car! 5. Once car hits bottom book, turn off timer.6. Check to make sure the timer left clear dots on the tape. If not, repeat.

If necessary, ask teacher for assistance.

Analysis:

1. Under the heading “Data” prepare a neat, ruler-drawn table with headings “Time (s)” “Position (cm)” and “Velocity (cm/s)”

2. Spread the ticker tape out flat. Examine the end where the dots are closest together. Find the first distinct dot.

3. Put a line through that dot. It is your origin. Then put a line through every 6th dot. Your lines now indicate the carts position every 0.1 seconds.

4. Place your tape against a metre stick with your “0” dot at the 0 cm mark on the metre stick. Then read off the position of each of your lines. Record these positions in your data table. The times will be 0, 0.1, 0.2, 0.3 …

5. Construct a “Position of the Car as a Function of Time” graph using your data. Remember title and labels. Use a “curve of best fit” for this graph.

19

0 1 2 3 4 5 6 1 2 3 4 5 6 1

t = 0 s t = 0.1 s t = 0.2 s

[Type here]

Calculations:

1. Use a tangent line to find the instantaneous velocity at a time near the beginning of the motion. Show your calculations neatly in a “Calculation” section in your lab report.

2. Repeat step 1 for a time near the middle of the motion3. Use your two velocities and the time between them to calculate the acceleration of the car.

Again, show this calculation in the calculation section of your report.

Conclusions:

1. State what you found the acceleration of the car to be.

2. We found the acceleration of the car by analyzing just two velocities. We are assuming then that the acceleration was constant. What analysis procedure could have we used in analyzing our position – time graph to make sure the car’s acceleration WAS actually constant?

3. Suppose the ramp had been steeper.a. What changes would have seen in our position – time graph? Answer this

question by making a sketch of a position – time with two curves on it; one representing your original data and one representing the data if the ramp had been steeper. Be sure to label which is which.

b. What would have we seen happen to the car’s acceleration?

20