Download Does frictional force depend on the size of the contact surface area?

Does frictional force depend on the contact surface’s normal force?
You will measure the frictional force (Ff) using two objects of different weights.
We measure 𝐹𝑓 by indirect means. In the case when
an object undergoes motion with a constant velocity,
the 𝐹𝑓 is equal in magnitude and in an opposite
direction to the applied force. Therefore, you measure
the 𝐹𝑓 by measuring the applied force when the object
is undergoing constant motion.
You will complete this experiment in two parts. For each part, repeat the measurement of the
𝐹𝑓 a total of six times and calculate the average 𝐹𝑓 :
 Part 1. Measure the mass of the block. Measure its FN.Pull the block until it is moving at
a constant velocity and measure the 𝐹𝑓 .
 Part 2. Add the weight to the block. Measure the mass of the combined block (with
added weight). Measure its FN.Pull the combined block until it is moving at a constant
velocity and measure the 𝐹𝑓 .
Block:
Block (with weight):
mass of block: 𝑚1 = _____________ kg
mass of block and weight: 𝑚2 = ________ kg
normal force : 𝐹𝑁1 = _____________ N
normal force : 𝐹𝑁2 = _____________ N
i
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2
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𝐹𝑓 [N]
̅̅̅̅
𝐹𝑓1 = ___________ N
i
1
2
3
4
5
6
𝐹𝑓 [N]
̅̅̅̅
𝐹𝑓2 = ___________ N

What is the ratio between the block and combined block’s normal forces?
𝐹𝑁2

What is the ratio between the block and combine blocks’ frictional forces?
𝐹𝑓2

What do you conclude about the relationship between frictional force and normal
force?
𝐹𝑁1
𝐹𝑓1
=
=
Does frictional force depend on the size of the contact surface area?
You will measure the frictional force (Ff ) using two blocks with differently-sized contact
surface areas (A).
We measure 𝐹𝑓 by indirect means. In the case when
an object undergoes motion with a constant velocity,
the 𝐹𝑓 is equal in magnitude and in an opposite
direction to the applied force. Therefore, you measure
the 𝐹𝑓 by measuring the applied force when the object
is undergoing constant motion.
You will complete this experiment in two parts. For each part, repeat the measurement of the
𝐹𝑓 a total of six times and calculate the average 𝐹𝑓 :
 Part 1. Position the block so that its larger surface area is face-down. Measure the mass
of the block. Pull the block until it is moving at a constant velocity and measure the 𝐹𝑓 .
 Part 2. Turn the block onto its side so that its smaller surface area is face-down.
Measure the mass of the block. Pull the block until it is moving at a constant velocity
and measure the 𝐹𝑓 .
Larger area:
Smaller area:
Larger surface area:
Smaller surface area:
𝐴1 = _____________ cm2
𝐴2 = _____________ cm2
i
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𝐹𝑓 [N]
̅̅̅̅
𝐹𝑓1 = ___________ N
𝐹𝑓 [N]
i
1
2
3
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̅̅̅̅
𝐹𝑓2 = ___________ N
𝑆2

What is the ratio between the blocks’ surface areas?

What is the ratio between the blocks’ frictional forces? 𝐹𝑓2 =

What do you conclude about the relationship between frictional force and the size of
𝑆1
=
𝐹
𝑓1
the contact surface?
Does frictional force depend on the type of contact surfaces?
You will measure the frictional force by using blocks with different types of contact surfaces.
We measure 𝐹𝑓 by indirect means. In the case when
an object undergoes motion with a constant velocity,
the 𝐹𝑓 is equal in magnitude and in an opposite
direction to the applied force. Therefore, you measure
the 𝐹𝑓 by measuring the applied force when the object
is undergoing constant motion.
You will complete this experiment in two parts. For each part, repeat the measurement of the
𝐹𝑓 a total of six times and calculate the average 𝐹𝑓 :
 Part 1. Pull the wood block until it is moving at a constant velocity and measure the 𝐹𝑓 .
 Part 2. Pull the sandpaper-covered block until it is moving at a constant velocity and
measure the 𝐹𝑓 .
Wood – contact surface:
i
1
2
3
4
5
6
𝐹𝑓 [N]
̅̅̅̅
𝐹𝑓1 = ___________ N
Sandpaper – contact surface:
𝐹𝑓 [N]
i
1
2
3
4
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6
̅̅̅̅
𝐹𝑓2 = ___________ N
𝐹

What is the ratio between the blocks’ frictional forces? 𝐹𝑓2 =

What did you observe happens when the contact surface is changed?

What do you conclude about the relationship between frictional force and the type of
𝑓1
contact surfaces?