forces. between which 2 points is the turtle accelerating? a) a & b b) b & c c) a & c d)...

ForcesForces

Between which 2 points is Between which 2 points is the turtle accelerating? the turtle accelerating?

a)a) A & BA & B

b)b) B & CB & C

c)c) A & CA & C

d)d) B & DB & D

Between which 2 points is Between which 2 points is the turtle staying still? the turtle staying still?

a)a) Before ABefore A

b)b) B & CB & C

c)c) Before Before A and A and between between B & CB & C

d)d) The turtle does not The turtle does not stay stillstay still

Forces Affect MotionForces Affect Motion

ForceForce = a = a pushpush or a or a pullpull


ForceForce = a push or a pull = a push or a pull

– forces have a forces have a strengthstrength and and directiondirection

– Forces are measured in units called Forces are measured in units called NewtonsNewtons ( (NN))

1 N 20 N

Small force pushing to the

right

Big force pushing to the left


BalancedBalanced forcesforces = = equal equal forces forces working on working on 11 object in object in opposite opposite directionsdirections

100 N100 NTotal (net) force on rope = 0 N

Rope’s motion does not change (it is in equilibrium)

-

ForceForce

UnbalancedUnbalanced forcesforces = = unequalunequal forces cause an object to forces cause an object to accelerateaccelerate

120 N100 NTotal (net) force on rope = 20 N to the right

Rope moves to the right (it is in disequilibrium)

-

Which box is Which box is experiencing unbalanced experiencing unbalanced forces?forces?

5 N10 N

A

5 N

10 NB10 N

10 N C 10 N

10 ND5 N

5 N

a)a) Box ABox A

b)b) Box BBox B

c)c) Box CBox C

d)d) Box DBox D

Which boxes have a total Which boxes have a total (net) force of 0 N acting on (net) force of 0 N acting on them?them?

5 N10 N

A

5 N

10 NB10 N

10 N C 10 N

10 ND5 N

5 N

a)a) A onlyA only

b)b) A & BA & B

c)c) A & CA & C

d)d) A, B & A, B & CC

What is the total (net) force What is the total (net) force acting on Box D?acting on Box D?

5 N10 ND5 N

a)a) 20 N to 20 N to the rightthe right

b)b) 20 N to 20 N to the leftthe left

c)c) 10 N to the 10 N to the rightright

d)d) 10 N to the left10 N to the left

What will Box D do?What will Box D do?

5 N10 ND5 N

a)a) Accelerate to the leftAccelerate to the left

b)b) Accelerate to the Accelerate to the rightright

c)c) Stay stillStay still

d)d) Explode Explode

Resistance ForcesResistance Forces

ResistanceResistance forcesforces = forces that = forces that go go againstagainst the the motionmotion of an of an objectobject

Which force is acting on the Which force is acting on the ball rolling across the ball rolling across the counter?counter?

a)a) Downward Downward force of gravityforce of gravity

b)b) Backward Backward force of frictionforce of friction

c)c) Upward force Upward force of the counterof the counter

d)d) All of these forces are All of these forces are acting on the ballacting on the ball


Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– FrictionFriction = force exerted when 2 = force exerted when 2

surfaces rub against each othersurfaces rub against each other



surfaces rub against each othersurfaces rub against each other SlidingSliding = solid surfaces slide over each = solid surfaces slide over each

otherothermotion

friction



surfaces rub against each othersurfaces rub against each other SlidingSliding RollingRolling = object rolls over a solid = object rolls over a solid

surfacesurface

F

M



surfaces rub against each othersurfaces rub against each other SlidingSliding RollingRolling Fluid Fluid = object moving = object moving

through a fluid (through a fluid (liquid or gasliquid or gas))

M

F


Resistance forcesResistance forces = forces that = forces that go against the motion of an objectgo against the motion of an object– FrictionFriction

SlidingSliding RollingRolling Fluid Fluid

– Force of friction depends on: Force of friction depends on: types of types of surfacessurfaces how how hardhard the surfaces push together the surfaces push together

When might you want When might you want to decrease friction?to decrease friction?

a)a) When driving on the When driving on the highwayhighway

b)b) When walking across When walking across a wet floora wet floor

c)c) When snowboarding When snowboarding in the Olympicsin the Olympics

d)d) When climbing a When climbing a steep hillsteep hill

How could you How could you increase friction?increase friction?

a)a) Polishing metal Polishing metal surfacessurfaces

b)b) Adding oil to the Adding oil to the gears on a bikegears on a bike

c)c) Wearing slick Wearing slick shoes shoes

d)d) Putting sand on Putting sand on an icy drivewayan icy driveway


Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– GravityGravity = force that = force that pullspulls objects objects

towardtoward each other each other


Resistance forcesResistance forces = forces that = forces that go against the motion of an objectgo against the motion of an object– GravityGravity = force that pulls objects = force that pulls objects

toward each othertoward each other– Force of gravity Force of gravity

depends on:depends on: objects’ objects’ massmass distance between distance between

objectsobjects


Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– Air resistanceAir resistance = a type of = a type of fluid fluid

friction that affects friction that affects fallingfalling objects objects

gravity

Air resistance


Resistance forcesResistance forces = forces that = forces that go against the motion of an go against the motion of an objectobject– Air resistanceAir resistance = a type of fluid = a type of fluid

friction that affects falling objectsfriction that affects falling objects– Force of air resistance depends on:Force of air resistance depends on:

Object’s Object’s surface areasurface area Object’s Object’s speedspeed

Skydiving video clip

gravity

Air resistance

When dropped, which When dropped, which object would experience object would experience the MOST air resistance?the MOST air resistance?

a)a) A flat sheet of A flat sheet of paperpaper

b)b) A wadded up A wadded up sheet of paper sheet of paper

c)c) A paperclipA paperclip

d)d) A tennis ballA tennis ball

forces. between which 2 points is the turtle accelerating? a) a & b b) b & c c) a & c d)...

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