Give reasons

1)Why needle sinks but a ship floats?

Needles displace more water than its weight. The weight of the needle is less than the weight of fluid displaced by the body. .Ship is hollow and empty space contains air, makes the average density of water is less than the average density of water and it floats on water.

Density of iron is more than density of water, therefore weight of iron nail is more than wt. of water displace  by it and nail sinks. While shape of iron ship is made in such a way that it displaces more weight of water than its own wight. Secondly the ship is  hollow and the empty space contain air which makes the average density of ship is less than that of water and hence ship floats on water.

2 ) Why you can smell hot food even if you are away from kitchen but not cold food?


We smell hot food from distance because of diffusion process , as rate of diffusion increases with increase in temperature. As hot food has more temperature , the particles gain kinetic energy and move with greater speed. Hence it spreads a greater distance

3 ) A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

It is a known fact that every matter we study has a different compositions. The intermolecular spaces are the reasons as to why a diver is easily able to cut through water. This is for the reason that the molecules are far from each other. Unlike the case of solids, where the intermolecular space is low, water allows a diver to cut through it just like we can but through gases also.

4 ) What Makes a Rainbow Curved?


A rainbow is curved because it reflects the round shape of the sun. Because you are on Earth, part of the sun is blocked, which why rainbows appear as a half or a quarter circle. If you were in an airplane and saw a rainbow below you, it would appear as a full circle.
The rainbow is actually always the same shape: it’s always a circle. The way a rainbow is formed is that, when the light goes into a raindrop, it kind of reflects around the back [of the raindrop] and, as it goes in and goes out, it refracts – it bends – because light goes slower in water than it does in air.
The Rainbow Curve. A rainbow is not actually shaped like a semicircle or an arc; that is simply the shape that we see. In fact, a rainbow is a circle, but we can’t see the full shape because the horizon cuts off the lower half. … The range of angles at which raindrops reflect is the real reason why rainbows are curved.

5.Why airplanes fly but not fall ?


Airplanes fly because they are able to generate a force called lift which normally moves the airplane upward. Lift is generated by the forward motion of the airplane through the air. This motion is produced by the thrust of the engine.
The figure below is a simple diagram of the four forces acting on an airplane – Thrust, Lift , Drag and Weight.

 Drag is the force produced by the resistance of the air to the forward motion of the airplane. Swish your hand rapidly side-to-side and you will feel that resistance on your hand.

Weight is the force created by the pull of gravity toward the center of the earth. You will feel the effect of this force if you jump up from the floor. Your weight will force you back down.
 
When the Thrust produced by the engine(s) is greater than the force of Drag, the airplane moves forward. When the forward motion is enough to produce a force of Lift that is greater than the Weight, the airplane moves upward.
 
While any part of the airplane can produce Lift, the most Lift comes from the wings.
Gravity and drag (air resistance, which is friction caused by air rubbing against the plane) try to pull the plane down and slow its speed. A plane must be built so that lift and thrust are stronger than the pull of gravity and drag by just the right amount. Lift from the wings is used to overcome the force of gravity.

6.How is Thrust Generated?
 
There are two basic types of airplanes – propeller driven planes and jet planes.
 

Propeller Driven Planes – Propeller driven airplanes use a propeller that is turned by some type of engine. Propellers are shaped just like the wings, and also generate lift, except that the lift is forward instead of up and is called thrust. Each propeller is made up of two or more blades. The first propellers were made of wood, but now most propellers now are made of metal.
 
Jet Planes – Jet planes do not have propellers. Instead, they have jet engines that move the airplane forward through another physical principal discovered by Sir Isaac Newton (1642 – 1727). This is Newton’s Third Law of Motion – “For every action there is an equal and opposite reaction.” You can think of a jet engine as a tube in which a liquid fuel (like the fuel diesel trucks use) is burned at high pressure with air from a compressor. The resulting heat forces the gases out of the back of the tube at high speed. In accordance with Newton’s Law, an equal force is applied in the forward direction, moving the engine (and the plane it is attached to) forward.

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