LAB SESSION
STATIC FRICTION
EXPERIMENT
MEASUREMENT
determine of µ s (static coefficient of friction)
static coefficient of friction
a small horizontal force => NOT MOVING
Newton's law: by a 2nd force = STATIC FRICTION FORCE
Max. static friction force = Min. acting force (need to start the motion) 🚩
- NOT a property of an object
- a property of a pair of contact surfaces
µ s: static coefficient of friction
Fs,max: max. friction force
N: normal force
Dry, non-lubricated surfaces:
- independent of the contact area
- proportional to normal force on the surface. ❓
Newton's second law: F R = 0
OR 
T: tension force in the string acting on the vehicle (read from dynamometer
N: normal force from plane on the vehicle
m.g: vehicle's weight
Resolving the vectors in x and y components
opposite direction
= magnitude
verification of Newton's law of equilibrium
read dynamometer
θ= 15°
θ= 25°
determine adjustment error on T
a prismatic object (at rest) on horizontal surface
At the equilibrium state
theta: angle b/w inclined plane and horizontal surface ❓
theta s: critical angle = theta at the instant the block starts sliding down 🚩
θ= 10°
verification of the vector character of a force
- position of the end of the spring
- directions of both forces (indicate the axis of both springs)
- magnitude of both forces
- magnitude and direction of the force
the block
plastic
9
10
14
11
12
bright metal
Angle (°)
9
9.5
8
dark metal
7
6
6
click to edit
rubber
32
30
30
small wooden block
24
22
27
23
with 100 g
23
26
26
26
200 g
23
22
22
big wooden block
22
24
25
27
with 100 g
with 200 g
20
25
25
26
23
24
25
white (plastic?) block
10
11
11
0.19
0.2
0.29
0.27
0.29
up
down
0.42
.43
.42
0.4
.39
.39
REPORT
conlcusion: errors