What do you observe when force is applied and removed from the plunger of the syringe containing air. Explain briefly
What do you observe when force is applied and removed from the plunger of the syringe containing air. Explain briefly
This is about pressure - the air inside of the syringe takes up some volume and exerts pressure on the plunger. If you keep the air inside from escaping by holding the nozzle closed, then the air will get concentrated to higher pressure as you push in the plunger - until the pressure inside the syringe is the same as the pressure you're putting on it with the plunger, at which point you can't push it in anymore, because the air pressure becomes stronger than your finger.
To simplify things, let's talk about the case of an "empty" syringe (a syringe with just air in it). Normally air is expelled from the nozzle of a syringe when we push the plunger in (if we don't block the nozzle). But when we block the nozzle, we don't allow air molecules to be expelled. To get an idea of what this implies, let's look at the ideal gas equation: PV = nRT. Even though our gas is not technically "ideal" it will still follow the basic proportionalities of this law. When we don't allow molecules to escape, we are holding "n" constant -- the number of moles of gas in the container. R and T are also constant. However, by pushing the plunger in, we are trying to reduce the volume (V) of the container. This means that the pressure (P) has to increase in order for the right hand side of the equation to be constant. Pressure is equal to a force over an area. So when the pressure increases, the force of the molecules bouncing walls of the container (including the plunger) is also higher. This means it takes more force on our part to push against these air molecules. So it gets harder for us to push the syringe in when there's higher pressure
| This is about pressure - the air inside of the syringe takes up some volume and exerts pressure on the plunger. If you keep the air inside from escaping by holding the nozzle closed, then the air will get concentrated to higher pressure as you push in the plunger - until the pressure inside the syringe is the same as the pressure you're putting on it with the plunger, at which point you can't push it in anymore, because the air pressure becomes stronger than your finger. |
| To simplify things, let's talk about the case of an "empty" syringe (a syringe with just air in it). Normally air is expelled from the nozzle of a syringe when we push the plunger in (if we don't block the nozzle). But when we block the nozzle, we don't allow air molecules to be expelled. To get an idea of what this implies, let's look at the ideal gas equation: PV = nRT. Even though our gas is not technically "ideal" it will still follow the basic proportionalities of this law. When we don't allow molecules to escape, we are holding "n" constant -- the number of moles of gas in the container. R and T are also constant. However, by pushing the plunger in, we are trying to reduce the volume (V) of the container. This means that the pressure (P) has to increase in order for the right hand side of the equation to be constant. Pressure is equal to a force over an area. So when the pressure increases, the force of the molecules bouncing walls of the container (including the plunger) is also higher. This means it takes more force on our part to push against these air molecules. So it gets harder for us to push the syringe in when there's higher pressure |
