This is a very general question. I am familiar with hydraulic or "bottle" jacks, and I think this is what your question is about. Hydraulic jacks have a pump to force hydraulic fluid into a hydraulic cylinder, which forces it to extend. This action is what raises whatever load you place it under. The fluid is usually pretty specific to the jack. Go to your local hardware store and ask for hydraulic jack oil. I have seen people use transmission fluid in a pinch (way out on the farm, miles from the store).
Jacks are for lifting or raising things. They can be screwed jacks or air jacks, or most commonly, hydraulic jacks.
jacks reaction to what?
Hungry Jacks is at Livingston , Bussleten
Hurchel Jacks was born in 1929.
Digby Jacks died in 2011.
Sam Jacks died in 1975.
Al Jacks was born in 1935.
Harry Jacks died in 1994.
Ball Jacks happened in 1993.
William Jacks was born in 1841.
William Jacks died in 1907.
Digby Jacks was born in 1945.