[Music] hi and welcome back to frees science lessons. co.uk by the end of this video you should be able to describe how to determine the densities of regular and irregular solid objects now this is a required practical and it could come up as an exam question so it's important that you learn the details in the last video we looked at density and we saw that the density of material tells us the mass mass for a given volume we calculate density using this equation the density equals the mass in kilog divided by the volume in me cubed the unit of density is kilog per M cubed and remember that you're not given this equation in the exam so in this video we're looking at how we can determine the density of objects now objects can be divided into two broad categories regular objects such as this Cube have got Dimensions which are easy to measure so we could easily measure the length of each side using a ruler with irregular object such as this vas we cannot easily measure the dimensions we're going to look at how to deal with irregular objects later so let's look at how to determine the density of regular object such as the cube remember that the density is the mass divided by the volume so first we need to determine the mass we can do that easily by using a balance such as this one imagine that thebe Cube has a mass of 0.5 kg now we need to work out the volume of the cube to do that we use a ruler to measure the length of the side like this the length of each side of this cube is 120 mm in other words 0.12 M the volume equals the length of the side cubed so .12 cubed gives us a volume of. 1728 M cubed putting the mass and the volume into the equation gives us a density of 28935 kg per M cubed to two decimal places so as you can see determining the density of a regular object is relatively straightforward but what about an irregular object such as the V we saw before in the case of a regular object we cannot easily measure the dimensions instead we determine the volume using a method called displacement so let's look at this now just like before we start by finding the mass of the object using a balance we then fill a Eureka can with water a Eureka can has a spout so the water can flow out of the can now we place the object into the water this will cause water to be displaced and it will flow out of the can through the spout we now measure the volume of water displaced using a measuring cylinder this volume is the same as the volume of the object so now we know both the mass of the object and the volume of the object that means that we can calculate its density remember that you'll find plenty of questions on this assess practical in my vision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe how to determine the densities of regular and irregular solid objects [Music]