give scientific reasons..?

Question

*weight of body is more at poles and less at equator.
*why is it dangerous to jump out of moving bus?
*rolling friction is less than sliding friction
*steam 100 degree C produces more severe burns then water at 100 degree C..
*a needle sinks while ship floats.
*the explosions produced in sun are not heard.
*it is difficult to start fusion reaction..

if u know even a single reason do post.serious answers only.abuse will be reported.

Answer 1

The other answer about the sun being too far away is wrong, because irrespective of the distance, you cannot hear sound through vacuum, which is what we have between Sun and Earth. Sound waves are mechanical waves and need a medium like air, water or a piece of wood to travel. Light is electromagnetic radiation and can travel through vacuum also.

Weight of body is more at poles and less at equator because the object is closer at the poles to the center of the earth and the gravitational force is thus higher. the formula for attraction between two masses (the object and the earth) m and M is given by F = m.M/r^2 where r is the distance between their centres.

When we are inside the bus, we also have the same veocity and thus momentum mV. When we jump out, our feet touch the ground and come to rest but the rest of the body continues to move forward because of inertia. Thus the need to conserve the momentum makes us lean too forward and we may fall face down and get hurt.

The area of contact is less in rolling compared to sliding and frictional force is proportional to the area of contact.

Steam at 100 deg C has the added latent heat of vaporisation compared to water at 100 deg C. Thus steam burns add more heat to the tissue than water burns and the severity is proportional to the input heat.

A needle sinks because its volume/weight ratio is not sufficient to keep it afloat but a ship floats because the volume of the water displaced and thus the buoyancy (lift) is more than the weight of the ship. The ship's area is spread out compared to its height and the ship is hollow inside, where as the needle is solid. A hollow needle with ends plugged to prevent water from going inside may very well float.

It is difficult to start fusion reactions because the pressure and temperature required are enormous and are difficult to create and control. Hydrogen bombs are uncontrolled fusion reactions. The Sun is a gigantic fusion reactor.

Answer 2

Weight of body more at poles: Rotation causes the earth to bulge somewhat at the equator, so standing at the equator you'd be farther from the center of gravity of the earth.

If you jump from a bus, you'll still be moving at the speed of the bus.

Google Van der Waals force. It only acts on the surface in contact, which is large for a sliding object and very small for a rolling one.

When water reaches 100 C, the temperature stops rising. It continues to absorb heat energy, though, until it boils. Steam at 100 C has more energy in the same mass.

A ship only sinks until it displaces the volume of water equal to its own weight, but the volume of a ship includes quite a bit of empty space giving the submerged part a combined density lower than water. A needle sinks because it's a solid with greater density than water. Although if a small needle is laid carefully on the water's surface, it will float because of surface tension.

Sound is not transmitted through a vacuum.

It's difficult to start a fusion reaction because of the intense compression required to keep the atoms in contact. In stars, this is overcome by gravity. In a fission bomb, the material is compressed with a focussed high explosive blast. If the blast isn't powerful enough, there's only a partial explosion and the bulk of the material will be flung apart, ending the reaction. Even so, you're only forcing the material together in order to let the neutrons from its own decay impact other atoms. In other words, you only need to bring the atoms within gunshot distance of each other. In a fusion reaction, you need to force the atoms together much more closely in order to start fusing the nuclei. The repulsive forces are consequently greater, especially once the reaction starts. So while a fission bomb requires the force of a high explosive to compress the material enough to react, a fusion bomb requires the force of a fission explosion to compress the material and hold it in that condition long enough to react.

Answer 3

Explosion on sun are not heard because sun is too far away.