D) Friction - force between 2 surfaces that oppose motion
Depends on:
1) ________________of each surface
2) __________________ that holds objects together
fs 1) Static Friction - force of friction that must be overcome to move
an object at _______________________.
fk 2) Kinetic Friction - force of friction that opposes a ____________ object.
Kinetic friction is ______________than static friction fk ____ fs
To find static friction: fs= us Fn To find kinetic friction: fk = uk Fn
fs = force of ____________________friction
fk = force of ____________________friction
Fn = _________________force (The upward resisting force)
Us = coefficient of _________________friction - "the ___________________number"
Uk = coefficient of ________________friction - "the ___________________number"
1. Relates to ___________________of surfaces in contact
2. Calculated experimentally
FRICTION force - vector always drawn _________________________1.
Friction Applied Force
*** At constant velocity: F applied _________________________
***** When object is moving on a horizontal surface: Fn = ________= _______
On a horizontal surface:
f s = ___________________ f k = ___________________
Question 1
If an object is moving on a horizontal surface and you doubled the weight force on the object, how would that change the kinetic friction force?
Answer - (Hint: weight force = normal force on horizontal surface. ) ____________
Question 2
On a horizontal surface
Static
Friction equation
Kinetic
friction equation
f s= Fn Us = ______________ f k= Fn x Uk = _________________
Look at the equations above.
1) What would happen to the kinetic friction (fk) if:
a) Uk (the roughness number) were halved?
Answer -
b) You doubled the weight force (F)? Answer - ______________
c) you turned the block on its' side?
FRICTIONAL PROBLEMS
***** Remember Fn = Weight = mg when the object is on horizontal surface
Ex) A 5kg Steel block is resting on a *horizontal table*. The coefficient of static friction (Us) is 0.75 and the Uk is 0.57.
c) What force must be applied to the object to keep it moving at constant velocity?
(Hint: F net = 0) Answer ____________
Momentum - the property of moving object has that makes it __________________.
Momentum = _________ x _____________
p = ____________________________
(kg . m/s)
a) _________________ quantity
b) p has same direction as ___________________
c) units - kg×m/s
1) Relationship between force and momentum
When a Force acts on a body it changes its' ___________________
Showing the mathematical relationship
p = m x v F = m x a
= ___________________ F = ___________________
F = ____ Force is the time rate of change in _____________________
Cross multiply and you get …….. = _________
The change in momentum that an unbalanced force produces on an object depends on
___________________the force acts on a body.
2) Impulse F x t = J
Combining all the equations
Write on your test immediately before answering questions
ex1) A 5kg mass has its velocity change from 8 m/s east to 2 m/s east. Find the objects change in momentum
ex 2) A 5kg mass moving with a velocity of 8 m/s east has an impulse applied to it causing its velocity to change to 20 m/s East.
Find the Impulse:
Find
the force if the impulse was applied for 3 sec.
ex 3) How long would it take for a net upward force of 100N, to increase the speed of a 50kg from 100 m/s to 150 m/s.
ex4) A 1.0kg ball traveling @ 4 m/s strikes a
wall and bounces straight back @ 2m/s.
Find ______
(a) = = ______________
(b) What is impulse applied to the ball?
(c) What is the impulse applied to the wall?