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Forces
Review
20 N
20 N
15 N 25 N
1) What is the net force for
the tug-of-war?
2) Will the rope move?
Why or Why not?
40 N
40 N
1) Net force = 0 N
2) No, the rope will not
move – the forces are
balanced.
Draw a free body diagram
showing which forces are
acting on bike rider who is
coasting down a hill.
Air resistance and rolling
friction slow down the bike,
while gravity accelerates it.
Give 2 examples of
FLUID FRICTION.
Air resistance, Water drag,
water on a slide, oil in a car
engine, oil on a bike chain,
greasing a cookie sheet,
zamboni-ing an ice rink.
.
Why does an astronaut
weigh less on the moon?
Hint – WHY would the force of
gravity be weaker there?
The force of gravity is weaker
because:
1) the moon is FAR from earth’s
gravitational pull.
2) the moon has much less MASS
than the earth.
Charlie is grocery shopping. He
pushes the cart hard and lets go.
Draw a diagram of the forces
acting on the cart after he lets go
of the cart. What will happen?
Air Resistance
Friction
The only force acting that affects
the motion of the cart is FRICTION.
Eventually, the cart will come to a
stop because of the unbalanced
force of friction.
Give 2 examples of
SLIDING FRICTION.
ANY two solid
surfaces touching…
Give 1 example where we would
purposely INCREASE friction.
Increasing friction:
sand on an icy driveway, snow
tires on a car, treads on your
sneakers, brake pads on a car…
An acorn and a leaf fall out of a tree
at the same time. Which will land
first? Explain why.
Bonus – draw a free body diagram
showing the forces…
The acorn will land first because
air resistance slows down the leaf.
Give 1 example where we would
purposely DECREASE friction.
Decreasing friction:
waxing your skis, oil on a bike
chain, bowling shoes, using a
handcart to move furniture, a sled
to move through the snow.