Experiment 3 Dynamics

Experiment 3 Dynamics 

Topic:Dynamics

Title:Coefficient of static friction.

Objective:To determine the coefficient of static friction between two surfaces

Theory:

Figure 2 shows a wooden block of mass m hooked on one end of a spring 
resting on a inclined plane with angle of inclination .

Figure 2

When the wooden block is being displaced down the inclined plane,it will return to its 
original position when released if thenet force up the plane exceeds the limiting friction
 down the plane.If the block just stay stationary when released, the net force up the plane
 is equal to the limiting frictional force down the plane.IfT is the tension of the spring and F is the limiting friction,then

T-mgsin θ=F and F=μR

Hence

T=mg(μcos θ+sin θ)  …………1

Where is the coefficient of static friction and R the normal reaction.

If a mass m' is hung vertically by the same spring and produces the same 
extension,then the tension

T=m'g

Where m'is the mass equivalent to tensionT.

From equation (1),

m'=m(μcos θ+sin θ) 

Apparatus:

1. A smooth plank as inclined plane.
2. Six wooden block,one of which has a smooth surface and a hook.
   

3. Triple beam balance
4. A soft spring 

5. A 50 g mass hanger
6. Five 100g slotted masses

7. A retort stand and clamp
8. A weight for stabilizing the retort stand
9. A pendulum bob
10. Thread
11. A half-metre rule

Procedure:

Part I: To determine the relationship between the mass equivalent m' 
and the length of the spring

(a) Hook one end of the spring on the retort stand and hang the 50 g mass hanger
 with a 100 g slotted mass at the other end of the spring. 
Measure the length,L of the spring and record the mass m' 
(the mass hanger and the slotted mass).

(b) Increase the mass m' and measure the corresponding length,L of the spring. 

(c) Tabulate m' and L

(d) Plot a graph of L against m'.

Part II: To determine the coefficient of friction between two surfaces 

(a) Weigh and record the mass of the wooden block which has a hook. 

(b) Set-up the apparatus as in Figure 2. Measure and record the angle 
of inclination θ.

(c) Displace the wooden block downward gradually until the block just moves 
upwards when released. Measure and record the length L of the spring.

(d) The mass of the wooden block could be increased by adding other wooden
 blocks on top of the first. Weight and record the new combined mass m of 
the block. Repeat step (c).

(e) Tabulate m,L, and m', where m' is the mass equivalent for length L obtained from 
the graph L against m' in part I.

(f) Plot a graph of m' against m.

(g) Determine the gradient of graph m' against m and hence calculate the coefficient of static friction ,µ.

Data:

Graph :