Page 81 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Examples
• Rubbing our hands makes a heat.
• When you go down the slide you create a sliding friction.
• Sand on a icy road.
• When a player falls and slides on the basketball court.
• The player slides against the ground aggressively to get the ball.
• Pushing an object across a surface.
Friction on inclined surfaces
When an object is at rest on an inclined plane as shown in the figure the force of friction is static in nature. The
direction of static friction is in upward direction as the block has the tendency to move downwards. As there is
relative slipping between the surfaces the force of friction is kinetic in nature.
The normal force can be found using the gravitational, or weight, force and the angle of the inclined plane. It is
given by F= mgcosθ, where m is the mass, g is acceleration due to gravity and θ (theta) is the angle.

Examples
• Ramps. • Stairs. • Slides.
• Anthills. • Slanted roofs. • Escalators.

Assignment

Examples
1 Weight of a machine vice placed on the table of machine tool is 20 kgf. What is the minimum horizontal bice
needed which will start it sliding, if the co-efficient Siding friction is 0.19

Solution:
Co-efficient of friction u=0.19
Normal reaction R=20~kgf.
Force of friction = µ .R

0.19 x 20 =3.8~kgf
Minimum horizontal force required = 3.8 kgf
2 A solid weighing 50 kg is placed on a solid surface. How Minimum horizontal force required to move the
block when coefficient of friction is 0.25 between the block and the surface.
Solution:
Normal reaction R=50kg
Coefficient of friction µ =0.25
Force required to move the block = µ.R
=0.25 x 50 =12.5 kg

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CITS : WCS - Mechanical - Exercise 6