Today I got a puncture, no problem…out with the jack, pump, pump, pump…car raised, tyre changed and off we go.
If I tried to raise the car without the use of a jack I’d have no success at all, none of us would unless you’re Superman.
So how does a jack work?
Your basic car jack works via good ol’ leverage. That big metal rod that you pump rests on a fulcrum very close to the car. You probably had to pump that thing several times to raise the car just a few inches. Levers (and all forms of mechanical advantage like pulleys) trade force for distance. A relatively low amount of force but a large distance on one end of the jack equals a very high amount of force and short distance on the other end.
Bigger jacks add hydraulics into the mix to provide even more mechanical advantage.
I should have mentioned it was a scissor jack I used and I pumped about 10-15 times before the wheel was clear enough off the ground to enable me to change it.
The metal rod aint that big, maybe 18" tops
Some jacks use a lever, like the one friedo describes, and you have to pump the lever handle many times to move the car little by little. Other jacks use a screw, and you usually have to crank the handle a lot to get similarly small movement by the car.
In either case, you’re using a “simple machine” (lever or screw) to increase your power.
As said earlier, this type of jack uses a screw to gain a mechanical advantage, instead of a lever. And I don’t think a screw is considered a simple machine, but it is based off a simple machine…the wedge. (A knife is also basically just a wedge.)
ETA: I guess I was wrong, a screw is a simple machine.
Usually it’s pretty simple. You just wait until they’re stopped at a light, you walk up and point your gun right at them and say “this is a car-jack.” Most people give up as soon as they see a gun.
I’m guessing this would be a bad time to mention its safer to use ther proper tool for the job at hand…
If I recall my high school physics, there are six simple machines: the inclined plane, wedge, and screw; and the lever, wheel and axle, and pulley.
So you could also lift your car with a block & tackle (pulleys), or by pushing it up a long, low ramp (inclined plane) but that wouldn’t be quite as convenient.
You remember your class correctly, but unfortunately, your class was wrong. Most science texts from high school down just parrot what every other text of the same level says, without regard to whether it’s right or wrong. Several of the textbook “simple machines” are actually the same thing, but there are also many other machines which can’t be broken down to the textbook six. Even recognizing that the inclined plane, wedge, and screw are all the same, as are the lever and the wheel, I could still probably come up with a dozen or more truly distinct simple machines.
To the OP, think of how far you moved that handle, compared to how far your car moved upwards. The ratio of those two distances is the same (neglecting friction and other inefficiencies) as the ratio of the force you exerted to the force the jack exerted.