Water fountains work due to the pressure exerted by water on the walls of the fountain pipe. It further depends on the force by which water enters the pipe.

No, he will need the same effort because even by placing it vertically there will be required the same amount of friction as friction does not depend upon the area of contact.

There are around 17 full grown trees to be cut to make one tonne of paper. This paper can be recycled 5-7 times and can be reused.

A force that appears due to physical contact of two objects is called contact force.

No, the force applied by both boys is equal. So, net force will be zero and hence friction force will not come into play.

Yes, when we place our palm in front of a moving ball, then the palm apply a force on the moving ball and stop it.

The three examples of inflammable substances are petrol, alcohol, LPG.

CO₂ can be stored in cylinders in liquid form.

Petroleum is called black gold due to its great commercial importance.

Food Corporation of India (FCI) is the Government Agency which procure food grains from the farmers.

The rabi crops are known as winter crops because they are grown in winter season, e.g. wheat, gram, etc.

When a force is applied on an object, it may change its speed. If the applied force is in the direction of motion, the speed of the object increases. If the force is applied in the direction opposite to the motion, then it results in a decrease in the speed of the object.

The harmful products formed by the burning of a fuel are as follows:
1 Carbon fuels release unburnt carbon particles, which are dangerous pollutants that cause respiratory disorders.
2. Incomplete combustion of carbon fuels gives carbon monoxide, a poisonous gas that can even kill a person sleeping in a closed room.

The threshed seeds are thrown slowly after raising it to a certain height in presence of air which separates chaff from the seeds. Due to gravity of earth the heavy seeds fall straight to the ground while the light chaff is blown a little farther away by wind. The density of the material is an important factor.

We know that friction is caused by the interlocking of the irregularities in the two surfaces. It is obvious that the force of friction will increase if the two surfaces are pressed harder. So it is easy to drag a mat when nobody is sitting on but difficult when someone is sitting on it but difficult when someone is sitting on it.

Blunt knife has larger area than of sharp knife. So less pressure will be on vegetable which makes it tough to cut.

Various constituents of petroleum and their uses:
(i) LPG: Fuel for home and industry.
(ii) Petrol: Motor fuel, aviation fuel, solvent for dry cleaning.
(iii) Kerosene: Fuel for stoves, lamps and for jet aircraft.
(iv) Diesel: Fuel for heavy motor vehicles and electric generators.
(v) Lubricating Oil: Lubrication
(vi) Paraffin wax: Ointments, candles, Vaseline etc.
(vii) Bitumen: Paints and road surfacing.

Outermost Zone: It is blue coloured part because complete combustion takes place in this part due to sufficient amount of oxygen. It is the hottest part of the flame.
Middle Zone: The colour of the middle zone is yellow because incomplete combustion takes place in this part due to the lack of oxygen. It is less hot than other part of the flame.

'Conservation' is a term used to described the prudent (careful and sensible) use of natural resources. The earth's natural resources that need to be conserved are air, water, soil, minerals, fuels, plants and animals.

A matchstick can burn a splinter of wood directly because it has low ignition temperature, whereas a matchstick cannot burn a log of wood directly as it has high ignition temperature. In order to burn a log of wood, a small fire is first started by burning straw (or dry grass), or paper by a matchstick, then the log of wood is placed over this fire. This fire heats the log of wood to its ignition temperature due to which it starts burning.

We should use these fuels only when absolutely necessary because
(i) it will reduce air pollution and thus lead to better environment.
(ii) it will reduce the risk of global warming.
(iii) it will ensure their availability for a longer period of time.

(a) The person was spraying special chemicals called weedicides on his crops to kill unwanted plants (weeds) in his field.
(b) The mouth of the person was covered to prevent the inhaling of poisonous weedicide.
(c) Jassi is observant, attentive, cautious and an intelligent boy.

We can protect wildlife by following methods:
(i) Hunting should be banned.
(ii) Priority should be given to wildlife conservation programme.
(iii) Overgrazing should not be allowed in the natural habitat of organisms.
(iv) National parks and sanctuaries should be created to protect wildlife.
(v) Education should be given to people about importance of wildlife.

The known reserves of these will last only a few hundred years is true, as we know that coal and petroleum are fossil fuels. It requires the dead organisms millions of years to get converted into these fuels. Excessive and injudicious use of these fuels leads to shortage of these fuels and their use is also linked to global warming. It is therefore necessary that we use these fuels only when absolutely necessary.

The supply of water to crops at different intervals is called irrigation. Various systems of irrigation are:
(i) Traditional methods: The water available in wells, lakes and canals is lifted up by
(a) Moat (Pulley system);
(b) Chain pump
(c) Dhekli and;
(d) Rahat (Lever system)
Pumps are commonly used for lifting water.
(ii) Modern methods:
(a) Sprinkler system: This system is more useful on uneven land. The perpendicular pipes, having rotating nozzles on top, are jointed to the main pipeline at regular intervals. When water flows through main pipes, it gets sprinkled on the crop as if it is raining.
(b) Drip system: In this system water falls drop by drop just at the position of the roots. It is the best technique for watering fruit plants, garden and trees

Three essential requirements to produce fire are as follows:
(i) Fuel
(ii) Air and
(iii) Heat to acquire the ignition temperature. The job of fire extinguisher is to cut off the supply of air or to bring down the temperature of fuel or both. The most common fire extinguisher is water. But water works only when things like wood and paper are on fire. For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide (C0₂) is the best extinguisher. CO₂ being heavier than oxygen, covers the fire like a blanket. Since, the contact between the fuel and oxygen is cut-off, so the fire can be controlled. The added advantage of CO₂ is that in most cases, it does not harm the electrical equipment.