In this video today, I'll be looking at the energy of the position. The energy one has because one is on top of a hill, gravitational potential energy, and the energy one has as a result of speed. Kinetic energy. We'll also be looking at momentum. Momentum being a product of mass and velocity. One can be zero for an objected stationary and it will be non-zero value for an object that is moving. Momentum is the tendency of an object at rest to stay at rest and an object in motion to remain in motion. What are some of the ideas we'll be looking at in this video from a fairly loose perspective? The hill provides gravitational potential energy. Going up a hill, a car has to use the accelerator. You have to put energy into the system to get the car to the top of the hill. Coming down the hill, you can just roll. You don't have to use the accelerator. In fact, to keep them going too fast, you may have to use the brakes. Once you've gained speed coming down the hill, you can simply roll. In fact, on this particular stretch of road, one can actually roll all the way down to Spanish wall, traffic permitting, and watching this speed limit. Once his car is rolling, he will tend to keep rolling. In fact, an object in motion will tend to remain in motion. So cars, at the top of the hill, they have gravitational potential energy. They have potential energy. They have potential to do what physicists call work, a different kind of work than labor, work is in the sense of expending energy that, worked on by a gravity on the car, speeds it up down the hill, and then, at the bottom of the hill, the car can just keep rolling. The tendency of things to stay in motion is momentum. The energy something has in motion, that's referred to as kinetic energy. Kinetic energy is the energy of motion. Gravitational potential energy is the energy of being in a particular position. Momentum is gained. As the car rolls down the hill, momentum is, we'll see, mass, time to velocity. It's the physical science definition of momentum. And once something is in motion, it tends to remain in motion. Motion includes the speed of zero, so when something is at rest, it tends to remain at rest also. The children's side is also a good example of the use of gravitational potential energy to generate kinetic energy and to change momentum from zero to a higher speed. Here I have a coconut. Coconut is on top of the slide. Right now the coconut has a momentum of zero, no speed, mass, time to speed of zero is zero. And it has gravitational potential and you have no kinetic energy. It slides down and as being a coconut does come to a stop. But some of the gravitational potential energy has become kinetic energy at the bottom of the slide. And a little bit more energy gained in the fall off the end of the slide. So the gravitational potential energy that the coconut had at the top becomes kinetic energy, which is then a little bit more complicated and real, lost a friction there at the bottom. People don't actually have wheels. So as an example of runners, they're very inexact example, a poor example at best. But for a runner, the runner requires more energy to accelerate and to maintain a constant in pace once running. The difference is probably not significant for a short. For anything but a short distance, as I've got a long distance runner, they spend very little time accelerating. But for sprinters, it requires more energy to get up to speed and then they maintain that maximum speed as long as they can. There is more energy required to accelerate to a speed than to simply maintain that speed and keep on going. And to some extent, that's why runners can run such long distances because once they're up at speed, there really is a sort of momentum factor to keep you rolling for one foot falling in front of the other. It's very inexact. It's not scientifically sound, but that's the idea. Once in motion, it is easier to remain in motion. When it rests, you tend to remain at rest. And well, fleshed those out more fully in a later section. But for now, this idea of momentum, mass and velocity, we've talked about velocity. For mass, a massive object has more momentum than a less massive object, so that a large rock, such as this, if I could get it moving, would be much harder to stop moving once going than a little pebble rolling down a hill. The two may be going down at the same speed, but the more massive one will have more momentum. That is an introduction to the concepts of momentum, gravitational potential energy and kinetic energy. These will be three of the concepts that we will be exploring in the activities this week. Momentum, gravitational potential energy and kinetic energy. A hill provides kinetic energy.