Transcript impulses

HW
Due
Place both in In Box
(POGIL page 2…… and the worksheet)
HW Worksheet – given out at end of class
Quest Jan 23 (B day)
***There is a REALLY GOOD review
PowerPoint on my website…***
Do 1.Take one and complete BOTH
Now SIDES.
May work with peers.
A bug and the windshield of a fast moving car collide.
Tell whether the following statements are true or false,
and EXPLAIN your reasoning:
a. The forces of impact on the bug and on the car are
the same size.
1.
2.
3.
4.
True
False
Not enough info
Not quite sure
TRUE!
FORCES COME IN
PAIRS!
A bug and the windshield of a fast moving car collide.
Tell whether the following statements are true or false,
and EXPLAIN your reasoning:
b. The impulses on the bug and on the car are the
same size.
1.
2.
3.
4.
True
False
Not enough info
Not quite sure
TRUE!
SAME FORCE,
SAME CONTACT
TIME
A bug and the windshield of a fast moving car collide.
Tell whether the following statements are true or false,
and EXPLAIN your reasoning:
c. The changes in speed of the bug and on the car are
the same size.
1.
2.
3.
4.
True
False
Not enough info
Not quite sure
FALSE!
COMMON
SENSE…DO YOU
NOTICE THE CAR
SLOW DOWN?
DOES THE BUG
NOTICE A
CHANGE?
A bug and the windshield of a fast moving car collide.
Tell whether the following statements are true or false,
and EXPLAIN your reasoning:
d. The changes in momentum of the bug and on the
car are the same size.
TRUE!
1.
2.
3.
4.
True
False
Not enough info
Not quite sure
m
Δv = m Δv’
Not to mention,
Impulse = change in
momentum, and we
already determined
they have the same
impulse…
Bug
Ft
m
Windshield
Ft
Δv
m
Δv
•Same Impulse
•Same change in momentum
•Diff. masses and velocity changes!
Does a larger force always produce a larger impulse on
an object than a smaller force? Explain.
No – not always!!
1.
2.
3.
4.
t
Yes
F
= Ft
No
(1 N) (100s) = (10 N)(5s)
Not enough info
100 Ns = 50 Ns
Not quite sure
YES/NO:____ EXPLANATION:
A fully dressed student with a backpack is at rest in the
middle of a pond on perfectly frictionless ice and must
go to shore. Can this be accomplished? Use KEY TERMS
to explain:
1.
2.
3.
4.
Yes
No
Not enough info
Not quite sure
Yes – throw the
backpack! Force =
Force, Impulse =
Impulse
HW – that was due today (workseet)
• Worksheet
• Texts open if needed
• 3 minutes to review with peers in the FRONT
of the classroom
– Gossiping/ being off task will result in you going
back to your seat and will guarantee the teacher
will call on you.
• Then, we are rapidly popcorning!
QUESTIONS ABOUT…
• 24 or 26?
• A bicycle has a momentum of 24 kg•m/s.
What momentum would the bicycle have if it
had …
• a.… twice the mass and was moving at the
same speed?
TWICE as much!
mv=p
.
4 6 = 24
So….
8 . 6 = 48
• A bicycle has a momentum of 24 kg•m/s.
What momentum would the bicycle have if it
had …
• b.… the same mass and was moving with
twice the speed?
TWICE as much!
mv=p
.
4 6 = 24
So….
4. 12= 48
• A bicycle has a momentum of 24 kg•m/s.
What momentum would the bicycle have if it
had …
• c.… one-half the mass and was moving with
twice the speed?
Same!
mv=p
.
4 6 = 24
So….
2 . 12 = 24
• A bicycle has a momentum of 24 kg•m/s.
What momentum would the bicycle have if it
had …
• d.… the same mass and was moving with
one-half the speed?
HALF as much!
mv=p
.
4 6 = 24
So….
4. 3= 12
• A bicycle has a momentum of 24 kg•m/s.
What momentum would the bicycle have if it
had …
• e.… three times the mass and was moving
with one-half the speed?
1.5 times as much!
mv=p
.
4 6 = 24
So….
12 . 3 = 36
• A bicycle has a momentum of 24 kg•m/s.
What momentum would the bicycle have if it
had …
• f.… three times the mass and was moving
with twice the speed?
6 times as much!
mv=p
.
4 6 = 24
So….
12 . 12 = 144
Recap
• Last class, we talked about impulse changing
momentum.
• This class (and the next 2 classes), we are
going to talk about what happens if that
impulse occurs during 2 scenarios:
– When bouncing occurs
– When a collision occurs
POGIL from last class – 10 minutes
• Take out your notes from last class and go to the
demo section. (Nerf Guns, Ping Pong Balls,
Toppling)
• You will be shown the Nerf Gun and Toppling
Demos, and you will get to try the Ping Pong
Demos.
• BEFORE THAT…. I want you to consider the
following question (write & answer in your notes)
– Would a head-on collision between two cars be more
damaging to the occupants if the cars stuck together or
if the cars rebounded (bounced) upon collision?
(Assume the time of the collision is the same.)
Would a head-on collision between two cars be more
damaging to the occupants if the cars stuck together
or if the cars rebounded (bounced) upon collision?
(Assume the time of the collision is the same.)
1. When the cars stick
2. When the cars
bounce
3. Doesn’t matter
either way
4. Not sure!
POGIL from last class
• Cross out pages 3 – 4 … look like this:
unless you want to challenge yourself to try what the Geo kids are
doing…then, feel free to try them at home and check! 
POGIL from last class – 10 minutes
1. You will be shown the Nerf Gun and Toppling Demos,
and you will get to try the Ping Pong Demos.
2. Then, working in the FRONT of the classroom, you
MUST answer all questions A through F
3. Please review your HW on the POGIL (page 2)
–
•
Ensure that EVERYONE understands not only WHAT the
solutions are, but WHY they are what they are…you should
be able to transfer your thought process to other questions
regarding similar concepts.
***NOT SURE/ QUESTIONS? ASK A TEACHER!!!***
1. Finish part G – Conclusion. 10 minutes to complete!
When is impulse larger?
(heads down hands up)
1. When objects
bounce
2. When objects don’t
bounce
3. Doesn’t matter
either way
4. Not sure!
Bouncing
• Impulses are greater when bouncing takes place
• Ft = ∆(mv)
• Falling flower pot hits your head
– Momentum stops
• Falling flower pot hits your head and bounces off
– Momentum is reversed.
• **Impulse to stop < impulse to “throw it back again”**
– 2(∆mv)
– Karate chop
– Pelton wheel
Bouncing
Think about a bouncing ball:
Before it hits the ground:
Speed = v
Momentum = mv
At the moment it hits
the ground:
Speed = 0
Momentum = 0
Impulse needed to stop
the ball = mv
After it leaves the ground:
Speed = v
Momentum = mv
Impulse needed to
accelerate the ball
upwoard = mv
Total Impulse = 2mv
Important point: It only takes an impulse of mv to stop the ball. It
takes twice the impulse (2mv) to make it bounce)
Just like the medicine ball exercise!!!
If the time of impact is long, the force will be milder. If the time
is very short, the force is powerful. When things bounce off an
object after hitting them, it is even more deadly in force
magnitude.
A rebound is a special type of collision
involving:
A rebound is a special type of collision
involving:
 a direction change
 which results in a velocity change.
A rebound is a special type of collision
involving:
 a direction change
 which results in a velocity change.
Observe that the greater the rebound
effect, the greater the…
A rebound is a special type of collision
involving:
 a direction change
 which results in a velocity change.
Observe that the greater the rebound
effect, the greater the…
 acceleration,
 momentum change,
 and impulse.
A rebound is a special type of collision
involving:
 a direction change
 which results in a velocity change.
Observe that the greater the rebound
effect, the greater the…
 acceleration,
 momentum change,
 and impulse.
The result of the direction change is a
large velocity change.
HW – that was due last class
• #11-13, p. 100
• Texts open if needed
• 3 minutes to review with peers in the FRONT
of the classroom
– Gossiping/ being off task will result in you going
back to your seat and will guarantee the teacher
will call on you.
• Then, we are rapidly popcorning!
HW – that was due last class
• #11-13, p. 100
• Texts open if needed – we are rapidly
popcorning!
• 11a) Visualize yourself on a skateboard.
When you throw a ball, do you experience an
impulse? Yes – push the ball, and ball
pushes you (force) for an
amount of time…force x time =
impulse!
HW – that was due last class
• 11b) Visualize yourself on a skateboard.
When you catch a ball, do you experience an
impulse?
Yes – push the ball, and ball
pushes you (force) for an
amount of time…force x time =
impulse!
HW – that was due last class
• 11c) Visualize yourself on a skateboard.
When you catch a ball, and then throw it back,
do you experience an impulse?
Yes – push the ball, and ball
pushes you (force) for an
amount of time…force x time =
impulse!
HW – that was due last class
• 11d) Visualize yourself on a skateboard. In
which of the scenarios do you experience the
largest impulse?
Catch and throw – it’s
1. Catch
like bouncing! More
2. Throw
velocity change, so
3. Catch an throw more momentum
change, so more
4. Same in all
impulse!
HW – that was due last class
• 12) Why is more impulse delivered when
bouncing occurs?
More velocity change,
so more momentum
change, so more
impulse!
Go to your test seats…
•
•
•
•
Normal quiz procedures apply
Open notes, not open books
No calc needed… cell phones OUT and SILENT
When done, quiz in basket upside down and
you may continue working on your HW
– (make your hypotheses and try them)
• Open notes quest on Ch. 7 on Jan. 23
HW – that was due last class
• 13) Why is the Pelton wheel an improvement
over a wheel with flat blades?
Go to your test seats…
•
•
•
•
Normal quiz procedures apply
Open notes, not open books
No calc needed… cell phones OUT and SILENT
When done, quiz in basket upside down and take a
copy of your:
1. “Momentum Conceptual review” (HW)
• Start working on this – it is HW!!!
2. And “Midterm Information”
• Read the “Midterm Information” sheet
tonight – we will answer any questions about
it next class