Solution:

Why Sportsmen Use Shoes with Spikes

Sportsmen use shoes with spikes to enhance their grip and traction on the ground. The spikes are small, pointed projections attached to the sole of the shoe. These spikes dig into the ground, providing more friction and preventing slipping. This is particularly important in sports like running, football, and athletics where quick movements and sudden stops are common.

The spikes help to distribute the athlete's weight over a larger surface area, reducing the chances of slipping during high-speed activities. In track and field events, such as sprinting, the use of spikes enables runners to push off the ground more effectively, increasing speed and performance.

Additionally, the design of the spikes is tailored to different types of surfaces. For example, longer spikes are used for softer surfaces like grass, while shorter spikes are used for harder surfaces like tracks.

Solution:

Who will have to apply a larger force and why?

According to Newton's second law of motion, force is given by the formula:

Force = Mass × Acceleration

Both Iqbal and Seema are pushing boxes on the same floor, so the acceleration in both cases is the same. However, since Seema has to push a heavier box, the mass of her box is greater than Iqbal's box. Therefore, to move Seema's heavier box, she will have to apply a larger force.

In conclusion, Seema will have to apply a larger force because the mass of her box is greater than Iqbal's box.

Solution:

Why Sliding Friction is Less Than Static Friction

Friction is the force that opposes the motion of two surfaces in contact. There are two main types of friction: static friction and sliding friction.

Static Friction: Static friction is the force that resists the initiation of motion between two surfaces that are at rest relative to each other. This friction must be overcome to start moving an object. It is generally greater because the microscopic irregularities on the surfaces are in a more "locked" or "interlocked" position, which requires more force to overcome.

Sliding Friction: Sliding friction, on the other hand, occurs once an object is already in motion. When the object slides over a surface, the microscopic irregularities on the two surfaces do not interlock as strongly as they did when the object was at rest. This results in a lower amount of resistance to motion compared to static friction.

Therefore, the key reason why sliding friction is less than static friction is that when an object is at rest, the surfaces are more tightly interlocked, making it harder to start moving the object. Once the object is moving, these interlocks are partially broken, reducing the resistance.

Solution:

1. Fill in the blanks.

• (a) Friction opposes the relative motion between the surfaces in contact with each other.
• (b) Friction depends on the nature of surfaces.
• (c) Friction produces heat.
• (d) Sprinkling of powder on the carrom board reduces friction.
• (e) Sliding friction is lesser than the static friction.

Solution:

1. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Write the word “CORRECT” in front of the correct arrangement.

• (a) rolling, static, sliding
• (b) rolling, sliding, static
• (c) static, sliding, rolling CORRECT
• (d) sliding, static, rolling

Solution:

Answer:

The force of friction acting on the car on different surfaces in increasing order will be:

Correct arrangement: (c) towel, newspaper, dry marble floor, wet marble floor CORRECT

Solution:

Direction of Frictional Force Acting on a Sliding Book

When a book is kept on a tilted desk and starts sliding down, the direction of the frictional force is opposite to the direction of motion of the book. If the book is sliding downwards, the frictional force will act upwards along the surface of the desk, resisting the motion of the book.

Solution:

Effect of Spilling Soapy Water on a Marble Floor

When soapy water is spilled on a marble floor, it makes the floor slippery. This happens because soap reduces the friction between your feet and the floor. Friction is the force that helps you walk without slipping. With less friction, it becomes more difficult to walk on the floor as your feet are more likely to slide. Thus, it would be more difficult for you to walk on the floor after spilling soapy water.

Solution:

Friction: A Friend and a Foe

Friction is both a helpful and harmful force in our daily lives. Here are some examples to show how friction acts as both a friend and a foe:

Friction as a Friend:

• Walking: When we walk, friction between our shoes and the ground helps us to move without slipping.
• Writing: Friction between the pen and paper allows us to write clearly and maintain control.
• Brakes: The friction between brake pads and the wheel helps to slow down or stop vehicles.
• Lighting a match: The friction between the matchstick and the matchbox causes it to ignite.

Friction as a Foe:

• Wear and Tear: Friction between moving machine parts causes them to wear out over time, leading to damage.
• Increased Fuel Consumption: Friction between the tires and the road reduces the vehicle's efficiency, leading to more fuel consumption.
• Heat Generation: Excessive friction between surfaces can generate heat, which may damage materials and parts.
• Slippery Roads: Friction may be too low on icy or wet roads, leading to accidents.

Solution:

Explanation of Why Objects Moving in Fluids Must Have Special Shapes

Objects moving through fluids, such as air or water, must have special shapes to reduce resistance or drag. When an object moves through a fluid, the fluid particles collide with the surface of the object. The shape of the object influences how smoothly the fluid flows around it, which affects the amount of resistance the object experiences.

If the object has a streamlined shape, the fluid can flow smoothly around it, reducing the turbulence and drag. A streamlined shape is one that tapers at the front and gradually narrows at the back, like the body of a fish or the shape of an airplane. This allows the fluid to move around the object with minimal disturbance, allowing the object to move faster and with less energy.

On the other hand, if the object has a blunt or irregular shape, the fluid is forced to move more turbulently around it, increasing drag and resistance. This leads to more energy being required to move the object through the fluid, making it harder to maintain speed.

In conclusion, special shapes like streamlined designs help reduce drag and allow objects to move more efficiently through fluids.