A perpetual motion machine is (as the name implies) a machine that moves perpetually; it never stops. Ever. So if you created one today and set it going, it would keep on going until the Big Freeze<span>. Calling that “a long time” is an understatement of epic proportions</span>
Answer:
All of them: change velocity, accelerate, change position
Explanation:
We can answer this question by using Newton's second law:
F = ma
where
F is the net force on the object
m is the mass of the object
a is the acceleration
We notice that when there is an unbalanced force on the object, 
, and therefore
whcih means that the object will accelerate.
But acceleration is the rate of change of velocity, v:
And so,
which means that the object will change velocity.
If the object is changing velocity, this means that it is also moving: therefore, the position of the object must be changing, so also the option "change position" is correct.
Some of these frictions depend on the Pressure, temperature of atmosphere.
Static Friction: This is the friction force when two objects in contact are not moving relative to each other. This friction is higher than kinetic friction.
Kinetic or Dynamic friction: this the friction force opposing the motion of objects, when two objects in contact are in motion relative to each other. It is less than the static friction. The two surfaces are rubbing against each other as they move.
Rolling friction: This is the friction when two objects are in contact and one object is rolling over the other - like a wheel on a road. The point of contact appears as stationary. The rolling friction is very less compared to static friction & dynamic friction.
Lubricated friction: this is the friction between two solid surfaces in contact with a layer of lubricant fluid flowing in between them. This friction is the least.
Fluid friction - viscosity : this is friction between two adjacent layers that are moving relative to each other at different speeds in a fluid. This is not high.
Internal friction: when an object is compressed and forced to deform, like in a piece of rubber, there is friction between the layers, that opposes this deformation.
Skin friction is the friction that opposes movement of a fluid across a solid surface. This is also called drag. When a coin is dropped in water, there is a friction called drag on the coin. Same is the case when a ball is thrown, a drag is experienced by the ball due to the drag of air.
The total amount of water on earth <u>remains the same</u>.
<u>Option: A</u>
<u>Explanation:</u>
The quantity of water on Earth remains the same now as it was in the Olden days. All water which is consumed by living things continue to be as part of the Earth's total water content.
The total amount is not exactly constant, as there are two fluxes of water between Earth and the rest of the solar system. There is a steady rain of water-bearing meteoroids hitting the planet, which slowly increases the amount of water. At the same time, molecules of water often dissociate in the upper atmosphere into hydrogen and oxygen due to ultraviolet light from the sun. Some of the hydrogen atoms have enough energy to escape from Earth’s gravitational field, and so are lost. This slowly decreases the amount of water.
In addition, tectonic plate subduction is constantly carrying water down into Earth’s mantle, and volcanoes are constantly spewing water out onto the surface again. The balance between the two processes can change considerably over time.
But all of these actions are meager compared to the total quantity of water on our planet, and two of them are in the opposite direction of the other two. So the overall change is insignificant, even when considered over long spans of geologic time.
