1. Do falling objects drop at the same rate (for instance a pen and a ball dropped from the same height) or do they drop at different rates? I know a feather floats down very slowly but I would think a heavy object would fall faster than a light object.
In presence of air resistance, two bodies of different masses dropped at the same rate from the same height reaches the ground at different time. The weight of the body acts on downward direction whereas the force of air resistance acts upward. For light object, the force of air resistance is greater but for the heavier object, it is lesser. So, the heavier objects fall faster than a light object in presence of air resistance. Hence, a feather floats down very slowly but a heavy object fall faster than a light object.
While if two bodies of different masses dropped at the same rate from the same height in the vacuum then both will reach the ground at the same time as there is no force of resistance which acts on that bodies.
2. Why can a person lie on a bed of nails and not be injured? What is this scientific theory called?
This is a trick used by most tricksters and the so called magicians. But it is a feat that can be performed by all. A bed of nails has a lot of them, more than hundred. When a person lie on it, his/her weight (downward force) is distributed over the tips of all of them, increasing the area of contact. So by the relation , the body surface will feel less pressure. The harm on the body, then will be obviously less. If the same action be done on a single nail, then see if the magic works or not!!
3. I know that gravity keeps us on the earth, but what prevents us from being pushed or pulled through the floor, earth, etc. (besides concrete, wood, and soil)? Does it have something to do with opposite forces?
Newton's law of gravitation states that "the force of attraction between any two bodies in this universe is directly proportional to the product of their masses and inversely proportional to the square of the distance between them".
Hence, the mass of the earth is infinitely greater than mass of us. Hence, the force of attraction between the earth and us is quite much bigger than the force of attraction between us & any other substances. So the resultant effect is that all the substances are pushed into the ground. The question is why not through the ground right into the center of the earth.
The phenomena is prevented by yet another significant phenomena on earth. That is the electrostatic force existing between any charged particle. As a person touches the ground, the electrons of the outermost atoms of the body will be in direct contact with the electrons of the outermost atoms of the ground. The decrease in their separation brings an increase in the electrostatic repulsive force in between them. So this force starts to act against the force of gravity, and puts the body in balance.
However, as in the case of water, if they are themselves weak enough to exert any such opposing forces, the bodies sink into them.
4. Can you compress a liquid (water)?
The question is very much against something students are taught at their junior level that liquids are incompressible and gases are. The terminology used here is a comparative term. There is no substance that can not be compressed if sufficient force is applied. It is not the matter whether the substance can be compressed or not. The core is whether there exists enough force to produce that compression. An ant might not be able to squeeze an air filled balloon, but humans can. So the balloon is incompressible for the ant but compressible for humans.
Similar is the case of liquid compression. A small force ensures the compression of gases, but liquid compression requires a lot of force. How this force is created is however impracticable in normal life and normal measuring instruments might not be able to measure them. Seeing nothing in a dirty glass does not mean that there are no germs.
5. How do you determine the distance of lightening from where you are standing using the sight of lightening and the sound of the thunder?
at approximately 186,000 miles per second while sound travels
at approximately 1100 ft. per second.
6. Why do your ears pop when you are in an airplane?
The outside of the eardrum is exposed to the pressure of the air where ever you may be located. That pressure is 14.7 pounds per square inch at sea level on a standard day.
7. What is the physics involved in skydiving?
There is quite a bit of physics involved in skydiving, but lets start with the basics. Once you leave the plane there are essentially only two forces acting on you: the Earth's gravity pulling you straight down, and friction with the air. The friction with the air mostly adds up to push in the opposite direction from the direction you are moving, so basically it pushes up on you and your equipment.
8. If there was a hole through the earth would you be stopped in the middle due to gravity or would you fall straight through?
All objects are attracted to the centre of the Earth.
9. What is a geo-stationary orbit? Are there any other orbits?
A geo-stationary orbit is an orbit of an Earth's satellite whose period of rotation is exactly equal to the period of rotation of Earth about it's polar axis (which is 23 hours, 56 minutes and 4.1 seconds) and whose trajectory is aligned with the Earth's equator.
10. An astronaut in a circling satellite released an object out of the satellite in space. Will this object fall on the earth? Explain.
The object will not fall on the earth. Due to inertia of motion, the speed of the released object will be equal to the speed of the satellite in all respects, which makes this velocity equal to the orbital velocity. This velocity does not depend on the mass of the satellite, so it will follow the motion of the satellite and will act as another satellite of the earth.
11. Where is the force of gravity stronger, on the top of Mt. Everest or at sea level?
of gravity is stronger at sea level. The gravitational force,
as explained by Newton's Law of Gravitation, is inversely
proportional to the square of the separation between the
two masses (or the separation between the centers of mass
for the two objects).
In the case of the earth, the force of gravity is greatest on its surface and gradually decreases as you move away from its centre (as a square of the distance between the object and the center of the Earth). Of course, the earth is not a uniform sphere so the gravitational field around it is not uniform. Instead the force of gravity will also vary according to the mineral or oil deposits underground. There is also a need to distinguish between 'gravitational acceleration' and 'acceleration of free fall' of which we are more interested in. In the case of the latter, the latitude of the place we are concerned with also matters because of the rotation of the planet.
12. As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction?
This is a good question
and one which is commonly asked by students when friction
is discussed. It is true that wider tires commonly have better
traction. The main reason why this is so does not relate to
contact patch, however, but to composition. Soft compound
tires are required to be wider in order for the side-wall
to support the weight of the car. softer tires have a larger
coefficient of friction, therefore better traction. A narrow,
soft tire would not be strong enough, nor would it last very
long. Wear in a tire is related to contact patch. Harder compound
tires wear much longer, and can be narrower. They do, however
have a lower coefficient of friction, therefore less traction.
Among tires of the same type and composition, here is no appreciable
difference in 'traction' with different widths. Wider tires,
assuming all other factors are equal, commonly have stiffer
side-walls and experience less roll. This gives better cornering
13. A car is traveling at 60mph collide with another car traveling in same direction. If instead it collides into a wall at 60mph. Which one has more damage?
The magnitude of damage depends upon force received by a car when it collides with another car or wall. If the magnitude of force is greater then there is more damage and vice-versa. The force F received by a car when it collides with another car or a wall is given by the relation: , (where, dP is the change in momentum and dt is the time taken for collision).
When a car collides into a wall at 60mph then the change in momentum takes place in very short interval of time. As a result it receives greater force. When a car collides with another car traveling in same direction then the change in momentum takes place in longer interval of time so, it receives less force than former. If a car is traveling at 60mph collide with another car traveling in same direction. If instead it collides into a wall at 60mph. Latter one has more damage.
14. If Newton's law of motion, which states that any object in motion will remain in motion, is true, then why is it that as a comet gets close to the sun and it melts, and a tail forms, and why wouldn't it be just a big ball of melted stuff?
Law of Motion actually states that a body in motion will remain
in motion UNLESS ACTED UPON BY AN OUTSIDE FORCE. In the case
of a comet, there are a number of outside forces acting upon
15. I was told by my Physics instructor that there is such a
thing as negative time. Is that true, or was he just pulling my
16. Does a car makes more pressure to the floor when it goes faster, or the car could fly if it goes even faster?
an interesting question. This kind of question shows that
you are thinking because on the one hand it seems to make
sense that the faster a car goes the harder it must push on
the floor to go fast. But on the other hand it doesn't quite
sound right. So, this kind of question shows that you are
thinking about what you are thinking and that is always a
good thing to do.
17. Why is simple harmonic motion 'simple'? Is there a complex harmonic motion?
If you look at a text on Simple Harmonic Motion in a physics book you see that 'Simple' refers to the ideal case where there is no friction, viscosity etc. Indeed, ideal cases are usually the simples in Physics. But many books also have parts on 'Damped Oscillations' and 'Forced Oscillations' but these are not considered as simple, because they are closer to real cases. Also the solutions to ideal case is the simplest, and the solutions to forced and damped oscillations are more complicated as one could expect.
18. Why doesn't friction depend on surface area?
a larger area of contact between two surfaces would create
a larger source of frictional forces, it also reduces the
pressure between the two surfaces for a given force holding
them together. Since pressure equals force divided by the
area of contact, it works out that the increase in friction
generating area is exactly offset by the reduction in pressure;
the resulting frictional forces, then, are dependent only
on the frictional coefficient of the materials and the FORCE
holding them together.
19. A pendulum is hanging in a lift and is oscillating. The lift is given a free fall. What will happen to the bob of the pendulum?
depends on the time when free fall starts. The bob will continue
to move it's angular motion without any change in its angular
speed -so the angular momentum- with respect to freely falling
20. According to Newton's third law, every force is accompanied by an equal and opposite force. How can a moment ever take place?
Moment is the 'rotating effect' of force. A body rotates or feels a moment when two forces are acting on it but are not in the same line, I.e. there is some distance between the lines of action of the two forces. However if they are acting directly against each other in the same line, they simply cancel or undermine each other and thus produces no moment.