Taken from - Chapter 10, sec. 2
 Your
word is Friction.
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When you ride a sled down a snowy hill, the
sled’s motion changes at the top of the hill,
down the side and then again at the bottom.
What causes the change in motion?
There are different forces acting on the sled
– those forces are gravity which makes the
sled speed up
- and friction which brings the sled to a stop at the
bottom of the hill.
Let’s look more at these two forces.
Remember - Force is a push or pull on
an object that can result in changing
that object’s motion.
 Remember - The strength of force is
measured in the SI Unit called the
newton.
 Since gravity is a force – it is also
measured in newtons.
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The strength of friction depends on how hard
the surface of the object and the surface the
object is on push together.
It also depends on the type of surface the
object has and the type surface the object is
on.
◦ Try this – rub your hands together very lightly and
then rub them together with more force – which
causes more friction?
 When you rub your hands together more forcefully.
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Friction acts in the direction opposite
of the direction of motion.
◦ So when your sled is sliding down the hill,
friction is working in an direction up the
hill.
◦ Without friction – moving objects would
just keep going until they hit something.

Static Friction – friction that acts on an object
that is not moving or is at rest.
◦ Example: Your desk is sitting on the floor right
now and is not moving, so the only type of friction
working on your desk is static friction.
◦ In your foldable :
 Put the term ‘static friction’ on the outside
 Put the definition on the inside flap
 Draw a picture on the inside on the part of the paper
directly across from the flap.

Sliding Friction – friction that occurs when
two surfaces slide over each other.
◦ Example: When you push your textbook across
your desk you have sliding friction working on both
the book and the desk.
◦ In your foldable :
 Put the term ‘sliding friction’ on the outside
 Put the definition on the inside flap
 Draw a picture on the inside on the part of the paper
directly across from the flap.

Rolling Friction – friction that occurs when an
object rolls across another surface.
◦ Example: When you ride a skateboard or bicycle on
the road.
◦ In your foldable :
 Put the term ‘rolling friction’ on the outside
 Put the definition on the inside flap
 Draw a picture on the inside on the part of the paper
directly across from the flap.

Fluid Friction – friction that occurs when a
solid object moves through a fluid, such as
water, air, or oil.
◦ Example: When you ride a surfboard through an
ocean wave.
◦ In your foldable :
 Put the term ‘fluid friction’ on the outside
 Put the definition on the inside flap
 Draw a picture on the inside on the part of the paper
directly across from the flap.

On a separate sheet of paper and without
looking at your foldable/notes - List and
describe the 4 types of friction.
 Your
word is Gravity.

Gravity is the force that pulls objects toward
each other.
◦ The Earth pulls on the moon which keeps the moon
in orbit around the Earth.
◦ Gravity also pulls on us to keep us on the Earth.
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The two factors that affect gravity are mass
and weight.
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Mass is the amount of matter in an object.
Weight is a measurement of the force of gravity
on an object.
Remember – mass does not change from place to
place because the amount of matter in an object
does not change with location.
Remember – weight does change from place to
place, such as here on Earth vs. on the moon,
because the force of gravity changes.
The moon has less gravitational pull than the
Earth, so an object would weigh less on the
moon.

In your notebooks – calculate the weight of
the following objects based on their given
mass:
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Notebook – 10 grams
Pencil – 0.5 grams
Desk – 10 kilograms
Textbook – 20 grams
Person – 50 kilograms
You may use a calculator if you have one.
 Your
words are Mass and
Weight.
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Free fall occurs when the only force acting on
an object is the force of gravity.
During free fall, gravity is an unbalanced
force which causes the object to accelerate.
Because the only force acting on an object in
free fall is gravity, all objects in free fall
accelerate at the same rate - the rate of
acceleration due to gravity.
The rate of acceleration due to gravity is
9.8m/s2.
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Objects falling through air experience a type of
fluid friction called Air Resistance.
Like all other types of friction – air resistance
works in a direction opposite of the falling
object. Therefore, air resistance works in an
upward direction.
◦ Try this:
◦ Drop a flat piece of paper from a height equal to the
height of your desk. Then drop a crumpled sheet of
paper from the same height.
◦ Which one experiences the most air resistance?
 The flat sheet will experience the most air resistance
because it has a larger surface area.
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We know that falling objects accelerate at the
rate due to gravity – 9.8m/s2.
However, air resistance increases with velocity.
◦ At this point the forces on the falling object will be
balanced, meaning there is no longer any acceleration.
The object keeps falling but at the a constant rate = no
acceleration.
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Terminal Velocity is the greatest velocity a falling
object reaches.
◦ Terminal velocity is reached when the force of air
resistance equals the force of gravity on the object, or
the object’s weight.
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An object that is thrown, instead of dropped
straight down, is called a projectile.
Projectile motion describes the motion of a
projectile.
NOTE: A projectile and an object dropped
straight down will reach the ground at the
same time.
This happens because both objects are acted
on by the force of gravity in the same way.
◦ See the picture on p. 348 in the textbook.

On a separate sheet of paper do the ‘writing
in science’ activity on page 348 in your
textbook.