This demonstration is looking at friction and when I've got on my trolley are three baskets identical and they've got different amounts of weight in them and I'm going to give this trolley a push and you have to decide which basket is going to move first. Is it the one with the most mass? Is it the one with the least mass? So it's up to you to decide. You ready? One, two, three. My goodness, they all moved the same. Now why is this? Well, the frictional force that's on them depends upon the mass of the object. So it's weight mass, it's weight force and the force that I apply provides an acceleration and the amount acceleration also depends upon the mass of the object. So we've got the frictional force and the acceleration and the force that I'm applying which causes the acceleration both depending on the mass and in this case then the mass is irrelevant. So as I do this, it doesn't matter what the weight of the object is, we still get the same acceleration.