0
$\begingroup$

https://youtu.be/KWAvj8ATXmE

at 2:43 , when he is testing the force by lifting a mass, does he experience the weight of the mass on his hand(as friction) or is it the atmospheric pressure force that lifts the weight?

$\endgroup$
0
$\begingroup$

He is holding the entire thing up with his hand on the syringe. The weight is attached to the plunger. The syringe is sealed so no more air can enter. As the weight pulls the plunger down, it increases the vacuum inside the syringe until the greater air pressure on the outer rear of the plunger is equal to the weight, there the weight cannot pull the plunger out further. This is similar to stretching and releasing a spring, pulling the plunger out creates a partial vacuum inside, let go of the plunger and the vacuum will pull it back.

$\endgroup$
  • $\begingroup$ So doesnt that mean the air pushing on the plunger carries the weight? $\endgroup$ – muyustan Nov 2 '19 at 7:37
  • $\begingroup$ @muyustan yes the greater air pressure outside the plunger equals the weight tied to it. $\endgroup$ – Adrian Howard Nov 2 '19 at 7:42
  • $\begingroup$ Then, the air pressure force lifts the weight already, why my hand too has to experience that force? $\endgroup$ – muyustan Nov 2 '19 at 11:04
  • $\begingroup$ It's buoyancy is negligible (though not quite 0), it does not float like a balloon, the vacuum pressure keeps the plunger from being pulled out and falling to the floor. As I said , he is holding it all up with his hand. If the syringe were replaced with a spring, it would stretch until spring tension equaled the weight, then it would not stretch anymore, but you would feel all the weight of it on your hand. $\endgroup$ – Adrian Howard Nov 2 '19 at 14:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.