What is the volume of a sphere with a radius of 5?
What is the volume of a sphere with a radius of 6?
Volume of a sphere applet
Plug 5 into the equation for volume of a sphere
Welcome to MooMooMath. Today we are going to look at spheres and how to look at both the surface area and the volume of a sphere. Surface area is very simple, if you look at a circle or a sphere there is a great circle on the inside and I just highlighted it in red. Now they call it the great circle because it can be drawn inside a sphere. What you are going to do is find the area of that great circle which is just π x r^(2 )and the surface area is kind of like on a beach ball the amount of plastic you would need to create the ball and it is just four times the great circle. So if you can find the area of the circle you just multiple it by four. So you have 4 x π and in this case the radius is 5 and this becomes 5 squared. So 5 squared is 25 and 25 times 4 is 100 and you just stick the π next to it so it becomes 100 π and it is surface area so the units are always squared. Now let’s shift over here and look at volume, which is a similar formula. It is four thirds times πr^3 and we will cube that. So all I need for this formula is the radius again. So the radius is five and we will cube it times π times 4⁄3 So 5 cubed is 5 times 5 times 5 which is 125 so 4⁄3 times 125 is 500 over 3 and don’t forget your π and your units are cubed because it is 3 dimensional so take your radius cube it and stick a 1 under it and multiple it by 4⁄3 and you get 500⁄(3 π units cubed) So let’s look at a cheat sheet
Surface Area equals 4 x πr^2
Volume of a Sphere equals Four thirds pi r cubed
In this example our radius is 6 and six squared is 36 and 36 times 4 is 144 π units squared
Now to find the volume use 3 as the radius so 3 cubed is 27 and 27 times 4⁄3 is 36π units cubed so those are the two formulas for volume and surface area of a cube.