Learning Doing, Talking, Writing and Drawing Apprenticing Students into the World of Science 2014 John Polias Lexis Education and Department of English, The Hong Kong Polytechnic University cien ce S S –

When we switch on the vacuum pump, the can collapses or we can say the can gets crushed. Why does the can get crushed? The can gets crushed because of a big difference in pressure between the inside of the can and the outside. to the vacuum pump open canclosed can Explaining why a can gets crushed © John Polias 2014 But why is there a big difference in pressure between the inside and the outside of the can ?

© John Polias 2014 air particles inside the can air particles outside the can to the vacuum pump Before we switch on the vacuum pump, the number of particles (above a square centimetre) outside the can is the same as inside the can. So, we can say that the pressure inside the can and the pressure outside the can are the same. Before we switch on the vacuum pump

to the vacuum pump the wall of the can The air pressure inside the can is the same as outside the can © John Polias 2014 Before we switch on the vacuum pump

© John Polias 2014 air particles inside the can air particles outside the can to the vacuum pump When the vacuum pump is switched on, it sucks up air particles from inside the container so the number of particles inside the can decreases. After we switch on the vacuum pump

to the vacuum pump the wall of the can The air pressure inside the can has decreased because of the vacuum pump The air pressure outside the can is now much greater than the pressure inside the can © John Polias 2014 After we switch on the vacuum pump

When the vacuum pump is switched on, the number of air particles inside the can decreases greatly. So, the air pressure inside the can is much less than the air pressure outside the can. This large difference causes the greater outside air pressure to crush the can. © John Polias 2014