- A. Stop moving
- B. Move with an increased speed
- C. Move with a decreased speed
- D. Move in a different direction
(a) stop moving
- A. The density of the liquid
- B. The height of the liquid column
- C. Both (a) & (b)
- D. None of the above
(c) Both (a) & (b)
- A. Pascal
- B. N m -2
- C. Poise
- D. Both (a) & (b)
(d) Both (a) & (b)]
- A. 76 cm of mercury column
- B. 760 cm of mercury column
- C. 176 cm of mercury column
- D. 7.6 cm of mercury column
(a) 76 cm of mercury column
- A. Hydraulic lift
- B. Brake system
- C. Pressing heavy bundles
- D. All the above
(d) All the above
- A. Grease
- B. Water
- C. Coconut oil
- D. Ghee
(a) Grease
- A. N m 2
- B. Poise
- C. kg m s -1
- D. No unit
(b) poise
Increases
Pascal’s Law
Surface tension
Torricelli
True. Pressure is defined as the force acting on a given area. Mathematically, pressure is calculated as the ratio of force to the area over which the force is applied, expressed as P = F/A, where P is pressure, F is force, and A is area. The SI unit of pressure is the pascal (Pa), which is equivalent to one newton per square metre. This definition is fundamental in understanding how forces are distributed over surfaces and is crucial in many applications such as hydraulics, pneumatics, and structural engineering.
True. A moving body will come to rest due to friction alone. Friction is a force that opposes the motion of an object and acts in the direction opposite to the velocity of the object. When friction is the only force acting on a moving body, it continuously removes the kinetic energy of the object, causing it to decelerate. Eventually, the object loses all its kinetic energy and comes to rest. This is observed in everyday situations, such as when a ball rolled on the ground gradually slows down and stops due to friction between the ball and the ground surface.
True. A body will sink if the weight of the body is greater than the buoyant force acting on it. The buoyant force is the upward force exerted by a fluid on an object immersed in it, and according to Archimedes' principle, this force is equal to the weight of the fluid displaced by the object. When the weight of the body exceeds the buoyant force, the net downward force causes the body to sink. Conversely, if the buoyant force is greater than the weight, the body will float, and if they are equal, the body will remain suspended in the fluid.
True. One atmosphere is equivalent to 1,00,000 newton force acting on one square metre. This is the standard atmospheric pressure at sea level, which is approximately 101,325 pascals or about 1.01325 bar. One pascal is defined as one newton per square metre, so one atmosphere equals approximately 1,00,000 Pa or 1,00,000 N/m². This pressure is the weight of the entire column of air above a unit area of the Earth's surface at sea level. Understanding atmospheric pressure is important in various applications including weather prediction, aviation, and industrial processes.
False. The correct statement is that rolling friction is slightly lesser than sliding friction. This is because when an object rolls, the contact area between the surfaces is reduced compared to sliding, where the entire surface is in contact. Rolling motion involves less deformation of the surfaces and less interlocking of irregularities, resulting in lower frictional resistance. This is why rolling objects experience less friction than sliding objects, making rolling a more efficient mode of motion.
True. Friction is the only reason for the loss of energy in most mechanical systems. When two surfaces move relative to each other, friction converts kinetic energy into heat energy, causing energy to be dissipated from the system. This energy loss due to friction occurs in all types of motion, whether rolling, sliding, or any other form of relative motion between surfaces. The heat generated by friction represents the mechanical energy that has been lost from the system.
True. Liquid pressure decreases with the decrease of depth. Pressure in a liquid is directly proportional to the depth below the surface. As you move deeper into a liquid, the weight of the liquid column above increases, resulting in greater pressure. Conversely, as depth decreases and you move toward the surface, the weight of the liquid column above becomes smaller, causing the pressure to decrease. At the surface of a liquid, the pressure is minimum.
True. Viscosity depends on the pressure of a liquid. Viscosity is the measure of a liquid's resistance to flow, and it is affected by various factors including pressure. When pressure on a liquid increases, the molecules are forced closer together, which increases the internal friction between molecules and thus increases the viscosity of the liquid. Conversely, when pressure decreases, the viscosity of the liquid decreases. Temperature also affects viscosity, but pressure is a significant factor in determining how easily a liquid flows.
In order of increasing magnitude, the correct arrangement is: Static friction, Rolling friction, Sliding friction. Static friction is the maximum frictional force and acts when an object is at rest and tends to prevent it from moving. Rolling friction is smaller than static friction and acts on rolling objects. Sliding friction is the smallest of the three and acts when an object slides over a surface. This ordering reflects the relative magnitudes of frictional forces in different types of motion.
Rolling, Static.
Buoyant force.
Given : Weight of a stone F = 500 No
Area A = 25 cm 2 = 25 x 10 -4 m 2
To find : Pressure P = ?
Formula :Pressure P = 20 x 10 4 N/m 2 (or) 20 x 10 4 Pa
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion
Correct explanation:
The weight of the bags falls on larger area of shoulder. So lesser pressure is produced.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion
Correct explanation :
It is due to the surface tension of water.
Force can change the static condition of a body.
If you squeeze a sponge, its shape changes.
If you pull a rubber band, it becomes longer.
Force can change the static condition of a body.
A rest rubber ball begins to move, when a force applied on it.
Player applies a force on the stationary football while taking a penalty kick is football match. The force applied by player makes the football move towards the goal.
When you touch a nail immediately after it is hammered into a wooden plank, you feel that it is hot. This happens because friction between the nail and the wood generates heat. As the hammer strikes the nail repeatedly, the kinetic energy of the moving nail is converted into heat energy due to the friction between the nail and the wooden plank. The friction force opposes the motion of the nail, and the work done against this friction is transformed into thermal energy, raising the temperature of the nail significantly.
Friction arises between the surfaces of two bodies in relative motion due to the interlocking of the irregularities present on the two surfaces. Even though surfaces may appear smooth to the naked eye, they have microscopic irregularities, bumps, and valleys on them. When two surfaces are in contact and move relative to each other, these irregularities interlock and resist the motion. The force required to overcome this interlocking of surface irregularities is what we call friction. The greater the roughness of the surfaces, the greater the interlocking and hence the greater the friction.
Two instruments that help to measure the pressure of a fluid are the manometer and the pressure gauge. A manometer is a simple device that uses a liquid column to measure pressure differences and is commonly used in laboratories. A pressure gauge is an instrument that directly measures the pressure of a fluid and is widely used in practical applications such as measuring tire pressure, gas cylinder pressure, and atmospheric pressure in various industrial and domestic settings.
One atmosphere is defined as the pressure exerted by a column of mercury of height 760 millimeters at sea level under standard conditions. This standard atmospheric pressure is denoted as 1 atm. The pressure exerted by this mercury column of 760 mm height is considered as the reference pressure of magnitude one atmosphere. This definition is based on the barometric measurement of atmospheric pressure, where a mercury barometer shows a height of approximately 760 mm when measuring standard atmospheric pressure at sea level.
Heavy bags are provided with broad straps to reduce the pressure exerted on the shoulders. Since pressure is inversely proportional to the area of contact, broader straps distribute the weight of the bag over a larger area of the shoulder. This larger contact area results in lower pressure on the shoulders, making it more comfortable to carry the bag. If narrow straps were used instead, the same weight would be concentrated on a smaller area, creating higher pressure and causing discomfort or pain to the shoulders.
Surface tension helps plants in the process of water transport through their vascular system. Water molecules at the surface exhibit surface tension due to cohesive forces between them. The xylem tissues in plants are very narrow, tube-like vessels that transport water from the roots to the leaves and other parts of the plant. Due to the surface tension of water and the narrow diameter of these xylem vessels, water molecules are attracted to the walls of the vessels and to each other, creating a phenomenon called capillarity or capillary action. This capillary action allows water to rise upward against gravity through the xylem vessels, even to great heights in tall trees. The adhesive forces between water molecules and the vessel walls, combined with the cohesive forces between water molecules themselves, enable this upward movement of water. Without surface tension and capillary action, plants would not be able to transport water efficiently from their roots to their leaves and other aerial parts.
Honey has greater viscosity than oil. Viscosity is a measure of a liquid's resistance to flow, and it depends on the thickness and internal friction of the liquid. Honey is a much thicker liquid compared to oil, meaning it flows more slowly and resists motion more strongly. The greater viscosity of honey means that more frictional force acts on it as it flows, making it more resistant to movement. This is why honey pours very slowly from a container, while oil flows much more readily. The molecular structure and composition of honey, with its high concentration of sugars and water, contribute to its higher viscosity compared to oil. Temperature also affects viscosity, with honey becoming even more viscous at lower temperatures and less viscous at higher temperatures.
Friction is a force that opposes the relative motion between two surfaces in contact, or prevents a stationary object from moving when a force is applied to it. It acts in a direction opposite to the direction of motion or applied force. Friction is a fundamental force that plays an essential role in our daily lives. One important utility of friction is in vehicle safety and control. Cars and buses are able to move safely on roads and come to a stop because of friction between the treaded tyres and the road surface. Without this friction, vehicles would skid uncontrollably and it would be impossible to drive safely. Another significant application of friction is in writing. We are able to write on paper with a pencil or pen only because of friction between the tip of the writing instrument and the paper surface. This friction creates marks on the paper as the pencil or pen moves across it. Without friction, the pencil would simply slide over the paper without leaving any mark, making writing impossible.
Friction can be minimised through several practical methods. The first method is by using lubricants, which are substances applied between surfaces to reduce friction between them. Common examples of lubricants include oil, wax, grease, and castor oil. These substances create a thin layer between the surfaces, allowing them to slide more easily over each other with less resistance. The second method is by polishing the surfaces to make them smoother. For example, on a carrom board, fine powder is sprinkled and the surface is polished to make it smooth so that the striker can slide easily across the board with minimal friction. Smoother surfaces have fewer irregularities and therefore less friction. The third method is by using ball bearings instead of allowing direct sliding contact between surfaces. Ball bearings are used in the hubs of bicycle wheels because rolling friction is significantly smaller than sliding friction. By replacing sliding motion with rolling motion through the use of ball bearings or similar devices, the overall friction can be greatly reduced, making the movement more efficient.
Pascal's law states that pressure applied to a confined fluid is transmitted undiminished in all directions throughout the fluid. This principle has several important practical applications in everyday life. The first major application is in hydraulic lifts used at automobile service stations. These lifts work by applying pressure to a fluid in a confined space, which transmits the pressure equally in all directions, allowing the lift to raise vehicles upward smoothly and safely. The second application is in automobile brake systems, which operate according to Pascal's law. When a driver presses the brake pedal, it applies pressure to the brake fluid, which is transmitted equally to all four wheels, causing the brake pads to press against the brake discs and stop the vehicle. The third application is in hydraulic presses, which are used to compress materials such as cotton or cloth into compact bundles that occupy less space. The hydraulic press applies pressure to a fluid that is transmitted to a large piston, which compresses the material with great force. These applications demonstrate how Pascal's law enables us to multiply force and perform useful work in various mechanical systems.
Ball bearings are used in a cycle hub because they significantly reduce friction compared to direct sliding contact between surfaces. When two surfaces slide against each other, the friction between them is called sliding friction, which is relatively large and causes energy loss and wear. However, when rolling motion is used instead of sliding motion, the friction is called rolling friction, which is much smaller than sliding friction. In a cycle hub, ball bearings (also called lead shots) are small spherical objects that roll between the axle and the wheel rim. As the wheel rotates, these ball bearings roll rather than slide, replacing the large sliding friction with much smaller rolling friction. This reduction in friction makes the wheel rotate more smoothly and easily, requires less effort to pedal the cycle, reduces wear and tear on the components, and increases the overall efficiency and lifespan of the bicycle. Therefore, ball bearings are an essential component in cycle hubs and many other mechanical devices where smooth rotation is desired.
Friction is a necessity in most of our day to day activities. It is desirable in most situations of our daily life.
We can hold any object in our hand due to friction.
We can walk on the road because of friction. The footwear and the ground help us to walk without slipping.
Writing easily with a pen on paper is due to friction.
Automobiles can move safely due to friction between the tyres and the road. Brakes can be applied due to frictional resistance on brake shoes.
We are able to light a matchstick, sew clothes, tie a knot or fix a nail in the wall because of friction.
Though it is giving a negative effect, in most of our day to day life friction helps us to make our life easy. So, it is called as “necessary evil”.
Disadvantages of friction:
Friction wears out the surfaces rubbing with each other, like screws and gears in machines or soles of shoes.
To overcome the friction an excess amount of effort has to be given to operate a machine. This leads to wastage of energy.
Friction can be classified into two basic types:
Static friction
Kinetic friction.
1. Static friction : The friction experienced by the bodies, which are at rest is called static friction. (E.g : All the objects rigidly placed to be at rest on the Earth, a knot in a thread.
2. Kinetic friction : Friction existing during the motion of bodies is called kinetic friction.
Further, kinetic friction can be classified into two:
Sliding friction
Rolling friction.
1. Sliding friction : When a body slides over the surface of another body, the friction acting between the surfaces in contact is called sliding friction.
2. Rolling friction : When a body rolls over another surface, the friction acting between the surfaces in contact is called rolling friction. Rolling friction is less than sliding friction. That is why wheels are provided in vehicles, trolleys, suitcases etc.
To understand about the frictional force between the layers of liquid in motion.
Materials required : Different kinds of liquid (coconut oil, honey, water, ghee), glass plates – 4 nos.
Procedure :
Take a small quantity of different kinds of liquid like coconut oil, honey, water and ghee etc., in a cup.
Place one drop of each liquid on a separate glass plate.
Next, gently raise one end of the glass plate, one by one, so as to allow the liquid to slide down the smooth surface of the plate.
Observe the speed of each liquid.
Observation:
Each liquid moves with a different speed. Water flows faster than other liquids. Coconut oil flows with a moderate speed. Ghee flows very slowly.
Inference:
Between the layers of each liquid, in motion, there is a frictional force parallel to the layers of the liquid. This frictional force opposes the motion of the liquid layers while they are in motion.
1. Using lubricants:
A substance, which reduces the frictional force, is called a lubricant. Example: Grease, coconut oil, graphite, castor oil, etc.
The lubricants fill up the gaps in the irregular surfaces between the bodies in contact. This provides a smooth layer thus preventing a direct contact between their rough surfaces.
2. Using ball bearing:
Since, the rolling friction is smaller than sliding friction, sliding is replaced by rolling with the usage of ball bearings. We can see lead shots in the bearing of a cycle hub.
Take a plastic bottle. Punch three holes on its side in the same direction, but at different heights. Now pour some water into it and let it flow through the holes. Observe the flow of water.
Inference:
The water comes out from all the holes with a different force and falls on the table at points that are at variable distances from the bottle. Water from the lowest hole comes out with the greatest force and falls at a point that is at the maximum distance from the bottle. Water from the topmost hole comes out with the least force and falls at the point that is at the minimum distance from the bottle.Reason:
This activity confirms that the pressure in a liquid varies with the depth of the point of observation in it.
It is not advisable to take a fountain pen while travelling in an aeroplane because of the change in atmospheric pressure at high altitudes. Fountain pens are designed and sealed in such a way that the air pressure inside them is balanced with the atmospheric pressure at sea level, which is approximately 101.3 kilopascals. However, as an aeroplane climbs to high altitudes, the atmospheric pressure outside the plane decreases significantly. Although the cabin is pressurised to some extent, the pressure inside the cabin is still much lower than the pressure at sea level. Since the pressure inside the sealed fountain pen remains at the original sea level value, it becomes much greater than the reduced air pressure in the aeroplane cabin. This pressure difference causes the ink inside the pen to be pushed outward, and the pen starts leaking. The ink may leak onto clothes, documents, or other belongings, causing damage and mess. Therefore, it is advisable to avoid carrying fountain pens during air travel or to use ballpoint pens instead, which are not affected by pressure changes.
Yes, there is a special device called a tribometer that can measure the magnitude of friction directly. A tribometer is an instrument designed specifically to quantify the frictional force between two surfaces in contact. It works by measuring the force required to move one surface against another under controlled conditions, allowing scientists and engineers to determine the coefficient of friction and other friction-related properties of different materials and surface combinations.
No, we cannot use water as a barometric liquid instead of mercury, despite water being cheaper and more readily available. The main difficulty in constructing a water barometer lies in the height of the column required to measure atmospheric pressure. Mercury is used in barometers because of its very high density compared to water. Since density and height of the liquid column are inversely related for measuring the same pressure, a water barometer would need to be approximately 13.6 times taller than a mercury barometer to measure the same atmospheric pressure. This is because mercury is about 13.6 times denser than water. A mercury barometer typically has a column height of about 76 centimetres at sea level, whereas a water barometer would require a column height of approximately 10.3 metres, which is impractically tall and difficult to construct, transport, and use. Additionally, water is more prone to evaporation, freezing at low temperatures, and contamination, making it unsuitable for use in a barometer. Therefore, despite the cost, mercury remains the preferred choice for barometric liquids due to its high density and other favourable properties.