Hydraulic Jacks

Definition

A hydraulic jack is a jack (a device used to lift heavy loads, like wheels of vehicles) that uses hydraulic power.

How they work

A hydraulic jack works on pascal's principle,i.e, when force is applied to an enclosed fluid, it moves in all directions undiminished. 

Let me explain this a little clearer with an example. Let's say we have two syringes (without the needle, of course) named A & B. Let's fill A with water. If we push the piston of A, the water will flow through the tube & go into B, hence pushing B's piston upwards. 

If something is placed on top of B's piston then it will be moved.

Hydraulic jacks work the same way.

So, the next you see someone on the road lifting their tires with a jack, you can walk up to them & tell them how their jack works ;-)   

Citations

https://www.thomasnet.com/articles/materials-handling/how-hydraulic-jacks-work

Time Travel

Definition

  
Time. What is it? The continuing and unlimited progress of existence and events in past, present and future.
Today, traveling is possible in the three dimensions (length,height,breadth). But, what about the fourth dimension (time)? That's where time traveling comes in. Time travel is basically moving to the past or future.  

Analysis

Time travel isn't very complicated at all. Simply explained; Albert Einstein said that the universe has a speed limit, the speed of light. Nothing can go faster than that.

Imagine you are traveling in a spaceship that moves at the speed of light. You travel in that spaceship for just a few days through space. On earth, that would equal to about a 100 years. If you come back to earth, your friends would have aged & your city or town would have changed so much that you probably wouldn't even recognize it. 
That's basically what time travel is. 

Conclusion
  
Time travel is not yet possible, but one day it might be. If it is, it'll be possible only to travel to the future. The 'PAST' is & will always remain a question mark.

Citations

https://www.google.com/search?ei=9VawWujKG5DUjwPJ15pA&q=time+travel+definition&oq=time+travel+&gs_l=psy-ab.3.0.0i20i263k1j0i131k1j0l2j0i131k1j0l5.1588.5773.0.7414.16.15.0.1.1.0.319.1476.0j7j1j1.10.0....0...1c.1.64.psy-ab..5.11.1624.6..0i67k1j0i131i46k1j46i131k1j35i39k1j0i131i67k1.142.ILrmiLoWgvo
https://www.youtube.com/watch?v=YgdacFRkiZ8