CH 7 and CH 8 Flashcards
What is momentum equation?
p=mv (my pigeon is from martha’s vineyard)
What are the units of momentum?
no special name. just kg*m/s
If two objects have the same velocity, the one with the larger mass has _____ momemtum
larger
if two objects have the same mass, the one with less velocity has _____ momentum
less
As velocity increases, momentum _____
increases
What is impulse? what is the symbol?
Change in momentum, or FORCETIME or MASSdelta V.
the symbol is DELTA P
(a force over an amount of time changes momentum)
what are the units of impulse?
no special name. same as momentum. kg*m/s
Give a clear example of impulse:
Since the mass generally stays the same.. you can view impulse as the thing that changes the velocity of an object. An impulse slows an object down, or speeds it up. Yes, force changes it.. but impulse measures how much. A force for 5 seconds changes it a little, the same force for an hour changes it more. Impulse helps us see the difference.
What is “FAT MAV?”
F delta T = m delta v (force * change in time = mass * change in velocity)
F = ma can be changed to what?
to FAT MAV: change the a to (delta v / delta t) so you get: F = m (delta V / delta T)
this is another version of fat mav.
What does “conservation of momentum” mean?
Momentum before = momentum after
What are the three conservation of momentum equations we use in this class? (along with the situations
mv+mv= mv + mv (separate before and after). (m+m)v = mv + mv (stuck before). mv+mv= (m+m)v (stuck after)
What changes the momentum of an object?
Applying a force over an amount of time (WHICH IS IMPULSE!!). Impulse changes momentum.
mv = Ft what does this say?
what is delta t?
Generally used when something crashes. momentum before = impulse (because all of the momentum is lost in a crash). Mass times velocity before = Force (time).
delta t is always just t. it is positive. time is not negative.
What is an elastic collision?
When all KINETIC energy is preserved (we solve problems like this, but in reality, energy is usually lost in sound and heat)
What is an inelastic collision?
When some momentum, some energy is lost through heat, sound, etc (stuck together)
What types of collisions do we usually consider when solving problems in class?
We assume they are elastic collisions (similar to how we often ignore friction).
Which causes more impulse, a 1kg ball hitting you at 10m/s and falling, or bouncing off your head and traveling back at 5 m/s?
A ball bouncing causes more of an impulse. Impulse is change in momentum. The ball that stops velocity only changes 10m/s (from 10 to 0), the bouncing ball goes from +10m/s to -5m/s, an overall change of 15m/s. The more the velocity changes, the more the momentum changes, which is a larger impulse!
When a cannon is fired, explain how momentum is preserved.
mv(cannon) + mv(ball) before is ZERO. It has to be zero after, so the momentum the cannon moves must be opposite the momentum of the ball to cancel it out, so they must have the same magnitide. so after the cannon fires, MV (cannon) = MV (cannonball).
How are FORCE and MOMENTUM different?
Force = mass (acceleration) where Momentum = mass (velocity)
What is work?
FORCE X DISTANCE (in the direction of the applied force). Measured in JOULES
W=F*D
(The Weiner is a Friendly Dog)
If you drag a block 20m with 5N or force, how much work did you do?
100 newton meters, or 100 JOULES
IF WORK=FORCExDISTANCE, then DISTANCE=
WORK/FORCE
IF WORK=FORCExDISTANCE, then FORCE=
WORK/DISTANCE
If you do 10 joules of work over 5 meters, how much force?
WORK/DIST= FORCE so 10 Joules/ 5 meters = 2 NEWTONs
If you do 20 joules of work using 5N of force, how far did you go?
WORK/FORCE=DISTANCE so 20 joules/ 5 newtons= 4 meters
If you are holding a barbell still, is there any work being done? is there any force?
No work, because there is no distance. There are forces, but no NET force. The forces are all balanced. The force your arm is holding it is equal to the force of gravity, so it isn’t moving.
What is tricky about force, work and direction?
In order for work to be done, it has to happen in the SAME DIRECTION of the force applied. So if you walk across a room holding a barbell, no work is done on the barbell because it doesn’t move UP.
What is POWER? (two ways)
WORK/TIME or FORCE*DISTANC/TIME. It measures the rate of work, how fast you can do the work
What is ENERGY?
Ability to do work. Like stored work.
What are the units of ENERGY?
JOULES - think of it as “work waiting to be done” or “stored work”
How is work different from energy?
WORK is being done, Energy is work waiting to be done, like a battery wating to be used.
How is work different from power?
Power is a RATE OF DOING WORK, basically, how fast you can do the work.
Work is force*distance, and power is an amount of work per unit of time. It is work/time.
What is the unit of work we use?
JOULE (newton*meter)
What is the unit of power we use?
WATT (joule/sec) or (newton*meter/second)
What is the unit of energy we use?
JOULE (newton*meter)
How is momentum different from energy?
momentum is a vector quantity, it has direction. Energy is a scalar quantity.
Explain FORCE units two ways
Newton or kg*m/s2
Explain POWER units three ways
WATT or joule/s or kg*m2/s3
Explain WORK units three ways
JOULE, or Nm, or kg*m2/ s2
Explain IMPULSE in two ways
kgm/s or Newtonsecond
Explain MOMENTUM in two ways
kgm/s or nothing. there is no other way. It is dimensionally equivalent to a Newtonsecond but we use that for impulse
What is potential energy?
mgh- non-moving stored energy. from HEIGHT.
What is kinetic energy?
MOVING energy. one half mass velocity squared.
Explain how potential is different from kinetic?
kinetic energy is MOVING energy, energy from its velocity, while potential energy is HEIGHT energy, energy from its position.
You lift 8kg up 5 meters, How many JOULES?
400 Joules
You lift 8kg up 5 meters in 4 seconds, how many WATTS of power?
100 watts
You lift 8kg up 5 meters in 20 seconds, how many WATTS of power?
20 watts
there are ______ of FORCE, ____ of WORK ,______ of POWER and _____ of ENERGY and _______ of MOMENTUM and _____ of IMPULSE
NEWTONS of force, JOULES of work, WATTS of power and JOULES of energy and kgm/s of MOMENTUM and kgm/s of IMPULSE (notice, no special unit for momentum or impulse)
EQN relating change in PE to change in KE
mg(delta h)= 1/2 m(delta v)2
Conservation equation
PEo+KEo = PEf +KEf or mgh+1/2 mv2 = mgh + 1/2 mv2 (notice the mass can cancel if it doesn’t change)
How much energy in a 25kg block 4meters high?
PE= mgh = 25104 = 1000 J
How much energy in a 4kg block traveling 3 m/s
KE = mv2/2 = 4*3^2 / 2 = 36/2 = 18 J
How much power if you move 50 kg 20 meters in 10 seconds?
P = Fd / t = 50*20/10 = 100 WATTS
WATTS measure ____
Power
NEWTONS measure____
Force
JOULES measure _____
Work and Energy
What are the two energies we talk about in this unit?
Potential (height) and Kinetic (speed)
what is your favorite class ever
Physics
Who is your favorite teacher ever?
Mr. Nystrom
What is delta V?
Vfinal - Vinitial = Vf - Vo
What is Vf and Vo?
Vf is FINAL VELOCITY, the velocity after.
Vo (vee naught) is INITIAL VELOCITY, or starting velocity, or velocity at beginning
