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?
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.