8. ACTIVITY A
“Push Mo Yan”
Comparing Movements of Objects on Different
Surfaces
At the end of the activity, I can:
A. Describe frictional force
Infer how friction affect movements of objects.
Explain the effects of friction.
Materials:
Block of wood hook
Spring scale rods
Sand paper tape
Baby powder
9. What you need to do:
1. Attach a piece of sand paper on one side of the block
of wood.
2. Hook a spring scale to the block of wood. Place the
wood on the table. (The sand paper should met the
surface of the table.)
3. Using a steady force, use the spring scale to pull the
wood across the table at a steady speed. Record the
force applied to pull the block of wood across the
table.
4. Remove the sand paper from the block of wood.
Sprinkle a small amount of powder on the table.
Repeat step 3.
5. Place several rods on the table. Place the block of
wood on top of the rods. Then repeat step 3.
11. What have you found out?
1. What affects the motion of the block of
wood?______________
2. What kind of friction is shown when you let the
block of wood with sandpaper slide on the surface
of the
table?____________________________________.
3. What kind of friction is shown when you let the
block of wood roll on
rods?______________________________________.
4. Under what condition was the frictional force
smallest?
5. How do rollers help in decreasing the amount of
force needed to pull the block of wood?
15. A moving object is
affected by friction.
However, the amount of
friction may vary
depending on the type
of surface the objects
gets in contact with.
16. Rolling Friction
Kinds of Friction
Sliding Friction
When an object rolls over a surface, rolling friction is
produced.
Ex. In cycling, the weight of the rider and the bicycle
presses the tires against the ground. This downward force
creates increased friction between the tires, giving tire
traction. If it were not for the friction, the tires could not
push on the road surface to drive the rider forward.
Sliding friction, also called dry friction, occurs when two
objects rub against each other or slide against each other.
Sliding friction is caused by chemical bonding between
surfaces.
Ex. When you move a block of wood on sandpaper, the
movement of the wood is affected. Friction occurs on the
surface of the wood and the sandpaper or even on the
surface of the table or floor. The block of wood moves
slowly, with more force needed to move it.
17. Fluid Friction
Kinds of Friction
Static Friction
Fluid Friction is friction between moving objects and a
liquid or between an object moving in the air. Objects
moving through fluid, either liquid or gas, experience
drag. This drag slows down the motion of the object.
Ex. Fluid friction occurs in a swimmer swimming in
water, a boat travelling in water, or an airplane in the air.
In a moving boat, drag acts between the surface of the
boat and the water and between the sails and the wind.
Static Friction occurs in stationary objects or at rest. It is
a kind of friction that prevents an object from moving
against surface.
Ex. Static friction is shown in a notebook or any object
placed on a table or any surface, which remains still.
Friction keeps a notebook from sliding off a table, even
when the table is slightly tilted. You can pick up an object
without the object slipping through your fingers because
of friction.
18. Friction allows us to grip things. You would be able to pick up anything with
friction. You can hold and squeeze a ball because of friction.
Desirable Effects of Friction
Friction helps people convert one form of motion into another. Friction allows people
to walk . You move forward because there is friction between the surface of your shoes
and the ground. Without friction, you will slip or fall and not be able to stand up. A
cyclist uses friction to move forward. The friction between her/his legs shoes and the
pedals and between the chain and gears is needed to move the bike.
Friction converts some energy into heat. Friction is needed to produce fire. When you
light a matchstick, friction is needed to change chemical energy in the matchbox and
matchstick into light energy. Without matches, you can also produce fire by rubbing
rubbing two stones ot sticks together.
19. Friction makes objects difficult to move continuously. There is friction
between the bottom or feet of furniture and the floor. When moving furniture,
friction is undesirable.
Undesirable Effects of Friction
Friction converts some energy into heat, noise and wear and tear on
materials. When a cyclist pedals on a bicycle, the energy exerted by the
cyclist in converted into noise and heat. Too much heat can cause the wear
and tear of the bicycle parts and reduce the efficiency of the bicycle. Excess
frictional heat could damage the machine and the breaking system. This will
result in periodic maintenance and replacement of some parts of the engines.
20. Multiple Choice: Read each item carefully. Circle the letter of the best answer.
1. Which has the greatest friction?
a. Polished floor
b. Sandy floor
c. Wet floor
d. Tiled floor
2. The boat sailing on the sea slows down. What kind of friction is acting on it?
a. Static friction
b. Rolling friction
c. Fluid friction
d. Sliding friction
3. Which of the following statements best describes friction?
a. It is a force that occurs between solids.
b. It is a force that occurs only on rough surfaces
c. It is a force that occurs between solids and liquids.
d. It is a force that occurs when surfaces touch each other.
21. 4. How can you best reduce friction between the bottom or feet of furniture
and the floor?
a. By smoothing the floor
b. By keeping furniture on their place
c. By applying lubricants like wax on the floor
d. By putting wheels or rollers on the bottom or feet of furniture.
5. Which shows that friction is undesirable?
a. Pushing furniture
b. Lighting a matchstick
c. Walking on wet floors
d. Using the breaks when approaching a stoplight
6-10. Give example of situations where friction is applied.
