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‫Hello and welcome this lecture.

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‫We're going to be using those functionality nodes to manipulate the objects in our scene on request.

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‫So if I hit a spacebar, I can make this cube bunny hop up and down.

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‫Let's dive in and see how this works.

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‫So it's all very well being able to get data out of objects in the scene.

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‫But what about making them do stuff?

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‫Well, what I would like to do is use our physics system here to add a force to an cube and make it

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‫jump up in the air or be the first thing that we do with our programming that actually allows it to

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‫act in response to something.

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‫Now, the way I want to do this is so that it does it in response to actually pressing a key.

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‫We've used this Begin Play event in the past.

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‫I want to introduce you to some new events here.

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‫What we're going to do is we're going to right click in the level blueprint and we're going to search

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‫for Space Bar.

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‫And you can see that gives us a keyboard event under the category keyboard event space bar.

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‫We can click on that and we're going to bring in a new event node that's this red one that tells us

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‫when something should happen.

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‫And you can see it has two execution pins, one for when the space bar is pressed and one for when the

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‫space bar is released.

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‫So let's use this, shall we, to actually print the mass of our cube so I can do this by selecting

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‫all these nodes, and I can shift click to select more.

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‫I can drag them down into place and I can drag from the pressed execution pin to the input pin of our

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‫print string node.

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‫And you can see that that's going to actually have two execution pins go into print string, which means

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‫that this can be executed either when the spacebar is pressed or when we begin play.

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‫So let's go ahead and hit play and see that actually works.

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‫So we've got the thousand that comes up when we begin play space bar and thousand comes up again.

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‫What I want to do is for this to actually apply a force upwards.

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‫Now in actual fact, we don't want it to apply a force, but we want to have it apply something called

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‫an impulse.

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‫Now, the difference between the two, in physics parlance, is that a force happens over a certain

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‫amount of time, whereas an impulse is instantaneous.

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‫So what we're going to do is we're going to delete our print string node and we're going to delete the

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‫get mass and the conversion node as well.

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‫But we're going to leave the cube and static mesh nodes.

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‫So we've got our static mesh reference.

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‫So if we pull off of this, we're going to look for something that can add an impulse to our cube.

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‫Now notice that when I'm doing this, the search menu here has got context sensitive switched on.

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‫And that's quite important because this means it filters down the nodes available to the ones that use

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‫the static mesh component object.

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‫So if I look for impulse in here and type in impulse, you can see there is an add impulse node here.

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‫There's a few of them, but there's an ad impulse one.

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‫Let's go ahead and get that.

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‫You can see it's got execution pins that tell us when we should add the impulse so we can go ahead and

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‫instantly connect this up to the space bar pressed execution node.

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‫So this should mean that the impulse will get added when the space bar is pressed.

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‫So we're doing this we're adding this impulse to the static mesh component, but there are other properties

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‫here on the node that we need to fill out, particularly the value of the impulse itself.

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‫Now this has three parts to it an X, Y and a Z.

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‫In fact, when we have these three parts, it's said to be a vector, but we'll get on to vectors in

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‫much more detail in a later lecture.

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‫Notice this X, Y and z actually corresponds to the x, y and z we get on our movement widget, on our

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‫cube, and also in the bottom left hand corner of our viewport.

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‫You can see there's an X, Y and Z.

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‫They're showing us which directions these values basically relate to.

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‫So what we can do is we can add in a value.

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‫If I wanted it to go up, I would use the Z direction and we can put in a value into here, such as,

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‫I don't know, 100,000 like this.

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‫Let's try that out.

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‫We'll go and hit play and hit our spacebar.

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‫Then at the moment nothing is happening.

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‫And the reason for that is that the value I've entered here is too small.

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‫So I'd like you to take the challenge to tweak the impulse to a value that actually jumps it up into

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‫the air.

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‫So try multiplying the mass by 100.

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‫You may find that that is in the right ballpark and at least gets the cube to move, then play around.

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‫With this value to get something that you like the look of and that acts in a way that's enjoyable to

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‫you.

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‫And what if you had added it to X and Y instead?

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‫What different effects do you get there?

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‫Pause the video and have a go.

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‫Okay.

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‫Welcome back.

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‫So we're going to try this out.

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‫I'm saying 1000 and I can actually do the multiplication right from within here using asterisk multiplied

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‫by 100 should give us the rough ballpark we play and hit our spacebar.

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‫You can see it's doing tiny little bunny hops.

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‫Not a great deal.

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‫And if I hit spacebar repeatedly, it starts to go a little bit higher in the air.

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‫So I'm actually going to multiply this whole value again by asterisk four.

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‫So four times the value hit play and then make it jump in the air.

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‫And that's a little bit more of a decent bunny hop that we're getting there now.

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‫The reason we had to multiply by the mass is because of this formula.

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‫That force is actually equal to a mass times and acceleration.

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‫So if we want a certain acceleration, we need to multiply it by the mass and that gives us the force

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‫required.

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‫There's also a similar equation for an impulse where actually if what you want is a change in velocity

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‫rather than an acceleration, then you essentially multiply that by the mass.

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‫So what I was saying is that I wanted to increase the velocity by 400, which in this case is four meters

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‫per second because Unreal uses centimeters as its main unit, then 400 multiplied by the mass of the

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‫cube, gives us the impulse required.

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‫However, I don't actually have to do that maths if I don't want to.

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‫If my desire is a change in velocity, then you see there's this little checkbox down at the bottom

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‫of the node which is labelled Velocity Change or val change for short.

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‫And if I check that it basically ignores the mass entirely and just applies whatever velocity I want

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‫so I can just type in 400 directly into the Z and that will apply a velocity of 400 in the upwards direction,

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‫400 centimeters per second.

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‫So if I go ahead and play, you can see that the impact is exactly the same.

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‫However, now, no matter what mass I set on the cube, it's still going to jump by the same amount.

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‫And the final part of the puzzle here is what if I had put this on the X or the Y instead?

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‫So if I cut it out of the Z and I put it into Z, Y and I maybe I cancel out Z to zero entirely, if

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‫I hit play and hit the spacebar, then you can see it's shifting it over to the side, over to the left,

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‫which is the Y direction.

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‫If I'd done it in the X, it would shift it forward, which is the X direction.

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‫So I'm just going to put that back so that it's just 400 in the Z direction.

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‫We can hit play to make sure that that's the case and we've got our bunny hopping.

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‫So in this lecture we've seen how we can use nodes to actually do something.

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‫We've also looked at vectors and forces and impulses a little bit to understand the physics of those

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‫systems.

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‫I'll see you in the next lecture.