Professor Dave here, let's talk about impulse and momentum. In chemistry we learned about the conservation of matter. Here in physics we learned about the conservation of energy. These concepts can be extended to formulate another law, and that is the law of conservation of momentum. momentum is a term we may be familiar with, but once again we must learn the rigorous definitions of these words, and linear momentum is defined as mass times velocity, which will be represented by the letter p. Momentum is a vector quantity as it involves a velocity vector being multiplied by the scalar value of the object's mass. This means momentum will be expressed with SI units of kilograms meters per second. In this case our everyday use of the word is fairly accurate, and we might say that as a ball rolls downhill it will gather momentum. This is true because its velocity will increase as the force of gravity accelerates it towards the ground. The more momentum the ball gathers the more difficult it will be to bring it to a stop, and an object in motion can therefore have a larger momentum by virtue of being more massive like a huge boulder, or also by moving at high velocity, like a tiny hailstone or meteorite falling from the sky. If we consider a car in motion, it too will have a momentum equal to mass times velocity, and if you slam on the brakes to avoid a collision, the car will skid a certain distance, because force must be applied over some duration of time to bring a moving object to rest. The heavier the car and the faster it was moving, the greater this factor will be. A small force acting over a long time will do it, like if you take your foot off the gas and let the friction from the road slowly stop the car, or a large force acting over a short time could do it like firmly applying the brakes to the tires. The force that is applied times the duration of time that it is applied is called the impulse, which will be measured in Newton seconds. The relationship between impulse and momentum is summarized in the impulse-momentum theorem. It states that the impulse, f delta t, is equal to the change in momentum, or delta p which can also be expressed as mv final minus mv initial. So if you apply some force to push an object for some duration of time that object will gain a proportional amount of momentum. If an object loses momentum it must be imparting some force to something else over some time period. Just as the work-energy theorem describes conservation of mechanical energy, the impulse-momentum theorem describes conservation of linear momentum. Another ramification of this theorem is that the force imparted on a moving object when it strikes some surface will be very large if the impact is instantaneous, and much less if the impact involves some time duration. If you fall off your roof onto the ground it will hurt, but if you fall onto a trampoline it won't be as bad because the change in momentum imparted on your body, instead of happening instantly, will be delivered over the entire duration of your contact with the trampoline's surface, as it stretches from the force of your fall. This is also why baseball players are taught to swing through the ball rather than stopping the swing upon impact. Because if contact is maintained between the bat and the ball for as long as possible, the maximum possible force will be imparted upon the ball. In the case of an object striking another object, total momentum will be conserved through the collision and the sum of the momenta of the two objects will be the same before and after the collision. The easiest example of this concept involves balls on a pool table. We will often observe that one ball has momentum while the other does not, and after the collision, the first ball has stopped and all of its momentum has been imparted onto the other ball. This type of scenario illustrates conservation of momentum. There is much more to discuss regarding collisions which we will go over in the next tutorial, but first let's check comprehension. Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always feel free to email me: