# 434244

## 434244

﻿To determine the coefficient of static friction between two surfaces

Objectives:
To determine the relationship between the mass of load and the length of spring.

To determine the coefficient of static friction between two surface.

Part 1: The relationship between the mass of load and the length of spring

Apparatus and Materials:
1 Retort stand
2 Spring
3 Slotted masses 200g with hanger
4 Meter rule

Setup:

Figure 5-1

Procedure:
1 Hook one end of the spring on the retort stand.
2 Hang the hanger with a 20g slotted mass at the other end.
3 Measure the length l1 of the spring, record the mass m1 of the load.
4 Increase the mass m1, measure the corresponding length l1 of the spring.
5 Tabulate l1 and m1.
6 Plot a graph of l1 against m1.

Part 2: The coefficient of friction between two surfaces

Apparatus and Materials:
1 A smooth plank as inclined plane
2 Retort stand
3 Wooden blocks
4 Electronic balance
5 Spring
6 Protractor
7 Pendulum bob
9 Plasticine

Setup:

Figure: 5-2

Theory:

If the wooden block is being displaced down the inclined plane, the block will return to its original position when released because the net force up the plane exceeds the limiting friction down the plane. The downward displacement is being reduced gradually until a stage where the block stays stationary when released. At this point, the force up the plane equalized the limiting friction down the plane.

If T is the tension of the spring, F is the limiting friction, and  is the coefficient of static friction, then

T- mg sin θ = F
T- mg sin θ =  mg cos θ

If T = m’g , where m’ = mass equivalent to tension T, then

m’g – mg sin θ =  mg cos θ m’ = m(  cos θ + sin θ)

Procedure:
1 Weigh the mass of wooden block with a smooth surface. Record down the mass.

2 Adjust the retort stand, to...