Important Notes for CBSE Class 8 Science Chapter 12 – Friction. Friction Class 8 Notes and Study Material Download in PDF form.
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Friction Notes | Friction Class 8 Notes | Friction Quick Revision | Friction Class 8 Quick Revision Notes | Science Class 8 Ch 12 Notes | NCERT Class 8 Science Chapter 12 Notes PDF.
Friction Class 8 Notes
- Friction: Friction is a resistive force.
- It opposes relative motion when two surfaces come in contact with each other.
- It is dependent on the nature of surface coming in contact.
- Friction acts in the direction opposite to the direction of applied force
- It acts on both the Surfaces.
- Spring balance: a device used for measuring weight of an object.
Factors affecting Friction
- If two uneven or irregular surface come in contact with each other, friction is generated.
- Smooth looking surfaces can have number of minute irregularities on them.
- These irregularities on the surfaces look into one another causing friction.
- On attempt to move any surface, the force applied tries to overcome interlocking.
- Rough surfaces have larger number of irregularities, So the force of friction is greater if a rough surface is involved.
- Polishing a surface makes it smooth thus reducing friction.
- If the interacting surfaces are pressed hard, the frictional force increases.
- Static friction: The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction.
- Sliding friction: The force required to keep the object moving with the same speed is a measure of sliding friction.
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Why is friction important?
- If an object started moving, it would never stop if there were no friction.
- Friction is important as it acts on the tires of the automobiles and the road, and helps in starting, stopping or changing the direction of motion.
- Day to day activities like writing, walking, driving, tying knot etc. all occurs due to friction.
- On the contrary friction wears out the materials whether like screws, ball bearings or soles of shoes etc. This makes it undesirable some times.
- Friction can also generates.
Increasing and Reducing Friction
- Interlocking of irregularities on surface creates bonds which generates friction
- Friction can be avoided to a great extent by use of lubricants.
- Due to use of lubricants Movement becomes smooth.
Rolling and sliding Friction
- Rolling friction: The resistance offered to motion, When one body rolls over the surfaceof another bodyis called rolling friction.
- Rolling causes reduction in friction.
- It is always easier toroll than to slide a body over another.
- Sliding Friction has replaced rolling by using ball bearings in most machines.
- Rolling friction is smaller than sliding Friction.
Fluid Friction:
- Air is very light and thin and exerts frictional force on objects which move through it.
- Water andother also exert force of friction whenobjects move through them
- Gases and liquids arefluids, thesefluids can exertforce of friction on objects in motion which pass through them.
- Drag is the frictional force exerted by fluids.
- The frictional force on an object in afluid depends on its speed, shape ,nature of object, with respectto the fluid.
- The object has to overcome this exerted by the fluid.
- This causes loss of energy.
- This loss can be reduced by giving objects special place.