hello everyone and welcome to this lesson on vertical projectile motion before we go any further let's analyze each of those three words carefully so vertical okay so that means we are moving in the vertical direction only a projectile the scientific definition of a projectile is the following it is an object that is acted upon by the force of gravity only okay so it's not like a rocket that is being shot up into the air because a rocket would have an engine a projectile is something like a ball that is thrown upwards into the air now if you throw a ball into the air the only force acting upon it is gravity uh but kevin we also have air resistance yes we do have air resistance but in grade 12 we ignore that okay air resistance does play a big factor in real life but we can still get a very good understanding of the way things work by ignoring air resistance if you go further to university and you do a physics course or engineering then you might start taking air resistance into account so this chapter is all about objects that are going to be moving in the vertical direction and the only force acting upon them will be gravity and then motion i'm not really going to go into that i mean that's very self-explanatory the objects are obviously moving so it's a vertical object with objects that are moving in the vertical direction and they only have gravity acting upon them in grade 10 and 11 you would have used these four equations over here these were called the equations of motion and they were scientific developments or equations that can be used whenever you have the following acceleration that is constant and your object must be moving in a straight line so for example you could use it over there over there over there as long as the acceleration is constant and you're moving in a straight line you wouldn't use it when you're moving like that and so if you're moving vertically you can also use those equations because that is still a straight line so in this chapter you are going to use these equations trust me you barely ever going to use that third one i mean that last one i never use it you will be absolutely fine just using the other three that are remaining now a big question i always get is kevin i don't have enough information i mean i don't even know what the acceleration of this object is i've got too many unknowns okay so there we have acceleration there we have acceleration guys what's super nice about this chapter is you do have acceleration always we know that objects that are thrown into the air above planet earth always accelerate at the same or with the same value that key value i hope some of you have it going through your head right now is 9.8 meters per second per second and that is that that value is a number that tells us the acceleration of an object let me explain what it really means though because a lot of students they use it but they don't really understand its implication let's say i'm standing on the ground and i throw a ball upwards at 39.2 meters per second notice i'm using a one because i'm not talking about acceleration what would happen to that ball think about this logically science is a very logical thing think about if you're standing outside and you throw a ball upwards what will happen to the velocity of that ball it'll decrease right so what this means is that the speed or the velocity of the ball will decrease at 9.8 meters per second every second and that's where we get the two from now i know a lot of you at home are going ah that makes sense i wish my teacher would explain it like that i know many of my students say that when i explain that part to them so after one second your ball is going to be traveling at 29.4 meters per second how did i do that i just minus 9.8 aft so that's after one second after another second the ball would be traveling at 19.6 meters per second that's after two seconds after three seconds you would be traveling at 9.8 and after four seconds you would reach a velocity of zero your object would then be at its highest point and it would start falling downwards and guess what its velocity would be after the next second 9.8 then positive 19.6 then positive 29.4 and then when hits the ground again it'll be back at 39.2 well kevin that's really interesting i know it works amazingly it always changes by 9.8 meters per second every second if you are on a different planet like if you were on mars or the moon that value would be different okay it's typically going to be smaller on the moon it's about 1.4 so if you had to throw an object upwards on the moon it would take a lot longer to slow down and so it would have the effect of appearing to be almost floating so please remember that in this chapter okay kevin what's the acceleration it's always 9.8 okay 9.8 downwards always down even if your object is going upwards what is happening to its speed or its velocity it's busy slowing down so velocity might be going upwards that's okay but acceleration that's always gonna be acting down so kevin can objects have velocity going in one direction and acceleration going in a different direction of course think about a car if you have a car that is busy driving this way at 30 meters per second when it sees a red light it's going to start slowing down the car doesn't start moving backwards but it starts slowing down that means it's accelerating to the left so velocity and acceleration can work in opposite directions and so that's all i wanted to explain for this video in this chapter these are the three formulas you're going to use acceleration you do have