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Lessons
- Crop Production & Management
- Microorganisms – Friends & Foe
- Synthetic, Fibers & Plastic
- Materials – Metals and Non Metals
- Combustion and Flame
- Conservation Of Plants And Animals
- Coal & Petroleum
- Cell Structure And Functions
- Reproduction In Animals
- Reaching The Age Of Adolescence
- Force And Pressure
- Friction
- Sound
- Chemical Effects Of Electric Current
- Some Natural Phenomena
- Light
- Stars And The Solar System
- Pollution Of Air And Water
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Question Bank
- Question Bank – Chapter 1 – Crop Production & Management
- Question Bank – Chapter 2 – Microorganisms
- Question Bank – Chapter 3 – Synthetic Fibres and Plastics
- Question Bank – Chapter 4 – Metals and Non Metals
- Question Bank – Chapter 5 – Coal & Petroleum
- Question Bank – Chapter 6 – Combustion and Flame
- Question Bank – Chapter 7 – Conservation of Plants and Animals
- Question Bank – Chapter 8 – Cell Structure & Functions
- Question Bank – Chapter 9 – Reproduction
- Question Bank – Chapter 10 – Reaching the age of adolescence
- Question Bank – Chapter 11 – Force and Pressure
- Question Bank – Chapter 12 – Friction
- Question Bank – Chapter 13 – Sound
- Question Bank – Chapter 14 – Chemical Effects of Electric Current
- Question Bank – Chapter 15 – Some Natural Phenomena
- Question Bank – Chapter 16 – Light
- Question Bank – Chapter 17 – Stars and Solar System
- Question Bank – Chapter 18 – Pollution of Air & Water
Friction
- Friction is caused by the irregularities on the two surfaces in contact
- The force of friction always opposes the applied force.
- Spring Balance is a device used for measuring the force acting on an object.
- In spring balance stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.
- Friction is caused by the irregularities on the two surfaces in contact.
- Force of friction will increase if the two surfaces are pressed harder.
- The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction.
- If an object started moving, it would never stop if there were no friction.
- The sliding friction is slightly smaller than the static, any object started moving, it would never stop if there were no friction.
- Friction can also produce heat.
- The substances which reduce friction are called lubricants.
- Friction can never be entirely eliminated. No surface is perfectly smooth. Some irregularities are always there.
- To reduce friction in order to increase efficiency. oil, grease or graphite is applied
- When one body rolls over the surface of another, the resistance to motion is called the rolling friction. It reduces friction.
- Rolling reduces friction.
- It is always easier to roll than to slide a body over another. That is the reason it is convenient to pull the luggages fitted with rollers.
- Fluids exert force of friction on objects in motion through them. The frictional force exerted by fluids is also called drag.
- Fluids exert force of friction on objects in motion through them.
- The frictional force on an object in a fluid depends on its speed with respect to the fluid.
- Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.
- Friction depends on the nature of surfaces in contact.
- For a given pair of surfaces friction depends upon the state of smoothness of those surfaces.
- Friction depends on how hard the two surfaces press together.
- Static friction comes into play when we try to move an object at rest.
- Sliding friction comes with play when an object is sliding over another.
- Sliding friction is smaller than static friction.
- Friction can be increased by making a surface rough.
- Friction is important for many of our activities.
- The sole of the shoes and the tyres of the vehicle are treaded to increase friction.
- The friction is sometimes undesirable.
- Friction can be reduced by using lubricants.
- When one body rolls over another body, rolling friction comes into play. Rolling friction is smaller than the sliding friction.
- In many machines, friction is reduced by using ball bearings.
- Fluid friction can be minimized by giving suitable shapes to bodies moving in fluids.
- Even those surfaces which appear very smooth have a large number of minute irregularities on them Irregularities on the two surfaces lock into one another.
- You saw that if you apply the force along the left, friction acts along the right.
- Finally it stops. Have you not seen a moving ball on the ground stopping after some time? Why do we slip when we step on a banana peel.
- It is difficult to walk on a smooth and wet floor
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Sound