You are provided with a wooden block to which a hook is fixed, a set of masses, spring balance, and other necessary materials. Using the diagram above as a guide, carry out the following instructions.
Record the mass \(m_0\), indicated on the wooden block.
Place the block on the table.
Attach the spring balance to the hook.
Pull the spring balance horizontally with a gradual increase in force until the block just starts to move Record the spring balance reading F.
Repeat the procedure by placing in turn mass m=200, 400, 600, and 800g on top of the block. In each case, read and record the corresponding value of F.
Evaluate M = \(m_0\) + m and R = \(\frac{m}{100}\) in each case
Tabulate your readings.
Plot a graph with F on the vertical axis and R on the horizontal axis
Determine the slope, s, of the graph.
State two precautions taken to ensure accurate results.
(b)i. Define coefficient of static friction.
ii. A block of wood of mass 0.5 kg is pulled horizontally on a table by a force of 2.5 N. Calculate the coefficient of static friction between the two surfaces.(g = 10ms\(^{-2}\))
Verified Correct Answer: .
Physical Principles & Numerical Solution
Observation /table of values
Mass mo = 400g.
S/N
mo(g)
m(g)
(M=mo+m)g
R = \(\frac{M(g)}{100}\)
F(N)
1
400.0
0.00
400.0
4.00
1.70
2
400.0
200.0
600.0
6.00
2.40
3
400.0
400.0
800.0
8.00
3.60
4
400.0
600.0
1000.0
10.00
5.20
5
400.0
800.0
1200.0
12.00
6.30
Slope, s = \(\frac{\bigtriangleup{F}}{\bigtriangleup{R}} = \frac{F_{2}-F_{1}}{R_{2}-R_{1}}\)
Slope (S) = \(\frac{6.4-2.3}{12.0-6.0}\)
S = \(\frac{4.1}{6.0}\) = 0.68
PRECAUTION; i
- Avoided parallax error in reading spring balance.
- Tapped the wood/load slightly to avoid sticking to the table.
- Repeated readings are shown in the table.
- Zero error of the spring balance.
(b)i. Coefficient of static friction: This is the ratio of the frictional force F (when the body is just about to move) to the normal reaction R (between the two surfaces in contact).
ii. \(\mu\) = \(\frac{F}{R} = \frac{2}{5}\) = 0.5
Source: Myschool Past Questions Archive (Record #60006)