How to make a simple electric motor at home

This video shows a simple method to build a simple version of an electric motor at home.



Note how Fleming's Left Hand Rule is used to explain why the wire coil rotates in the presence of the magnetic field due to the pile of magnets!

Would a person get hurt or die if he lies on a bed of nails?

If your answer is yes, watch the following video featuring the world-renowned magician Criss Angel as he attempts to lie on a bed of coarse nails with a heavy vehicle on top of him!




How is it plausible that Criss did not even have a piercing wound on his back with all the weight acting on him?

The key lies in the fact that there are many nails on the nail bed which increases the surface area in contact with Criss' back. From our understanding of pressure (= force / area), pressure is reduced when the area increases. Moreover, the nails are broad and this has the effect of increasing the area of the sharp points in contact with Criss as well.

Hence, having the right number of nails to "defray" the weight (force) ensures that the pressure of his body weight on the nails do not get high enough to induce piercing. This allows Criss to preserve his life and keeping as a dare-devil magician! Criss is a magician who understands Physics and the concept of pressure well...

Old Tablecloth Trick

Have you ever wondered what will happen to several plates which lie on a table when a person pulls the tablecloth out quickly?

Watch the video for the answer.



If you are puzzled as to why the plates did not fall off the table with the tablecloth, then you should read up on the physics concept of inertia.

In physics, inertia is the tendency of an object (with mass) to resist a change in its motion or state of rest. Therefore, for an object which is at rest, it will always remain at rest, unless a resultant force is applied directly to the object.

The plates on the table were at rest initially. Hence, they would remain at rest when the tablecloth is pulled out so quickly that the frictional force between the cloth and underside of the plates cannot come into effect (hence there is no direct resultant force acting on the plates). The plates will remain at rest at their original positions.

How strong is your faith in Principle of Conservation of Energy?

Watch the following interesting video. Do you think the swinging concrete rock, released at the same height as the man's head but on the other side would hit the man when it is allowed to swing towards the man?




The answer lies in energy conservation.
The swinging rock can be likened to a pendulum.
When the rock is swung from its highest point, at that initial release point, all of the energy is gravitational potential energy.
As the rock swings, some of these gravitational potential energy (GPE) is converted to kinetic energy (KE) until the lowest point of its swing when all of the GPE is converted to KE.
As the rock continues in its swing, it ascends (gains in height). Hence, part of its KE is converted to GPE.
At the end of the swing, all of the KE from the lowest point has been converted to GPE.

This amount of GPE is EQUAL to the GPE at the initial release point by energy conservation (assuming energy loss to the surroundings is negligable or non-existent).
Since GPE depends on height, therefore the height the concrete rock can reach CANNOT BE HIGHER than that at the initial release point.

Therefore, the rock will never hit the man if it is released from rest initially at the other end of the swing!

Physics works!

Some Physics behind Sumo Wrestling

The following video provides an introduction to the popular Japanese sport of Sumo Wrestling.



Why does the Sumo Wrestler maintain a "Bottom-Heavy" Body and wrestles with legs wide apart?

Remember the objective in order to win is to be able to knock the opponent down or out of the ring. Therefore, it is of paramount importance that the body of each individual sumo wrestler be made as stable as possible.

Recall the two conditions of increasing stability:
Increase the base area
Lower the centre of gravity

Hence, the reason why the wrestlers maintain a "Bottom-Heavy" Body is to ensure that centre of gravity is made as low as possible.

Also, the reason the wrestlers stand with their legs apart is to increase the base area of their bodies.

With these two factors considered, they can improve their stability and increase their chances of winning the match! =)

The Physics behind the secret of Tightrope Walking

Have you ever wondered why some people can walk on tightropes without falling off?



The secret lies in the way they position themselves on the rope.
Whatever positions tightrope walkers adopt on the tightrope, they would do it such that their centre of gravity is always in line vertically with the point of contact (pivot) between their legs and the rope.

In this manner, their weight cannot exert a moment about the pivot (because perpendicular distance = 0) to cause them to turn and topple to either side of the rope!

Can you see how useful the physics principles you learn in school are!

Would a fat or skinny man float better on water?

Try to think of your answer before watching the video. [Hint: You can use density to explain the answer.]



Note that the density of fats is lower than that of that of muscles and bone.

Therefore, for the fat person who has a higher proportion of fats in him compared to muscles and bones, the average density of his body will be comparatively less than that of the skinny person.

Hence, the fat person finds it easier to float on water!