Does frictional force depend on the contact surface’s normal force?
You will measure the frictional force (F f
) using two objects of different weights.
We measure an object undergoes motion with a constant velocity, the 𝐹 𝑓
𝐹 𝑓
by indirect means. In the case when
is equal in magnitude and in an opposite direction to the applied force. Therefore, you measure the 𝐹 𝑓
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
𝐹 𝑓
a total of six times and calculate the average
𝐹
: 𝑓
 Part 1. Measure the mass of the block. Measure its F
N
.Pull the block until it is moving at
. a constant velocity and measure the 𝐹 𝑓
 Part 2. Add the weight to the block. Measure the mass of the combined block (with added weight). Measure its F
N
.Pull the combined block until it is moving at a constant velocity and measure the 𝐹 𝑓
.
Block: mass of block: 𝑚
1
= _____________ kg normal force : 𝐹
𝑁1
= _____________ N i
1
2
3
4
5
6
𝐹 𝑓
[N]
𝐹 𝑓1
̅̅̅̅ = ___________ N
Block (with weight): mass of block and weight: 𝑚
2
= ________ kg normal force : 𝐹
𝑁2
= _____________ N i
1
2
3
4
5
6
𝐹 𝑓
[N]
𝐹 𝑓2
̅̅̅̅ = ___________ N
 What is the ratio between the block and combined block’s normal forces? 𝐹
𝑁2
𝐹
𝑁1
=
 What is the ratio between the block and combine blocks’ frictional forces?
𝐹 𝑓2
𝐹 𝑓1
=
 What do you conclude about the relationship between frictional force and normal force?

Does frictional force depend on the size of the contact surface area?
You will measure the frictional force (F f
) using two blocks with differently-sized contact surface areas (A).
We measure an object undergoes motion with a constant velocity, the 𝐹 𝑓
𝐹 𝑓
by indirect means. In the case when
is equal in magnitude and in an opposite direction to the applied force. Therefore, you measure the 𝐹 𝑓
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
𝐹 𝑓
a total of six times and calculate the average
𝐹 𝑓
:
 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 𝐹 𝑓
.
 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 𝐹 𝑓
.
Larger area:
Larger surface area:
Smaller area:
Smaller surface area:
𝐴
1
= _____________ cm 2 i
1
2
3
4
5
6
𝐹 𝑓
[N]
𝐹 𝑓1
̅̅̅̅ = ___________ N
𝐴
2
= _____________ cm i
1
2
3
4
5
6
𝐹 𝑓2
2
𝐹 𝑓
[N]
̅̅̅̅ = ___________ N
 What is the ratio between the blocks’ surface areas?
𝑆
2
𝑆
1
=
 What is the ratio between the blocks’ frictional forces?
𝐹 𝑓2
𝐹 𝑓1
=
 What do you conclude about the relationship between frictional force and the size of 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 an object undergoes motion with a constant velocity, the 𝐹 𝑓
𝐹 𝑓
by indirect means. In the case when
is equal in magnitude and in an opposite direction to the applied force. Therefore, you measure the 𝐹 𝑓
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
𝐹 𝑓
a total of six times and calculate the average
𝐹 𝑓
:
 Part 1. Pull the wood block until it is moving at a constant velocity and measure the 𝐹 𝑓
 Part 2. Pull the sandpaper-covered block until it is moving at a constant velocity and measure the 𝐹 𝑓
.
.
Wood – contact surface: Sandpaper – contact surface: i
1
2
3
4
5
6
𝐹 𝑓
[N]
𝐹 𝑓1
̅̅̅̅ = ___________ N i
1
2
3
4
5
6
𝐹 𝑓
[N]
𝐹 𝑓2
̅̅̅̅ = ___________ N
 What is the ratio between the blocks’ frictional forces?
𝐹 𝑓2
𝐹 𝑓1
=
 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 contact surfaces?