2 Which one is more likely to float? BuoyancyWhich one is more likely to float?wwRoughly thesame sizehhThis bowling ballOr this balloon?Your students probably already understand some of the basics…
3 Buoyancy Density = mass/volume Even though they are the same size (dimensions),the balloon will float because it is less dense than the fluid around it!Density = mass/volume
4 Buoyancy“Any body wholly or partially immersed in a fluid experiences an upthrust equal to, but opposite in sense to, the weight of the fluid displaced.”THIS GUY“Any body wholly or partially immersed in a fluid experiences an upthrust equal to, but opposite in sense to, the weight of the fluid displaced.”According to legend…King Hiero II gave a goldsmith an amount of pure gold to construct a crown. After the crown was delivered the king became suspicious that the craftsman had stolen some of the gold and mixed the rest with silver. He asked Archimedes to determine if this was true without melting the crown.While taking a bath, Archimedes noticed that the level of the water in the tub rose as he got in, and realized that this effect could be used to determine the volume of the crown. The submerged crown would displace an amount of water equal to its own volume. By dividing the mass of the crown by the volume of water displaced, the density of the crown could be obtained. This density would be lower than that of gold if cheaper and less dense metals had been added.Archimedes then took to the streets naked, so excited by his discovery that he had forgotten to dress, crying "Eureka!" (meaning "I have found it!"). The test was conducted successfully, proving that silver had indeed been mixed in.Was Archimedes buoyant?!
5 Archimedes looked at forces BuoyancyArchimedes looked at forcesBuoyancy: upward force on an objectGravity: downward force on an objectPressure: force all around an objectGravityThe ability to float.PressurePressureBuoyancy
6 Archimedes principle simplified BuoyancyArchimedes principle simplifiedDownward forceequal to the weightof the objectA body immersed in a fluid experiences a buoyant force equal to the weight of the fluid it displacesUpward force (buoyant force)equal to the weightof the displaced fluid
8 Buoyancy Remember these? Density = mass/volumeWhen the density of the object equals the density of the water around it, the object is neutrally buoyant
9 Play with these concepts Archimedes loves neutrally buoyant ROVs BuoyancyPlay with these conceptsArchimedes loves neutrally buoyant ROVs
10 So how do we make our ROVs neutrally buoyant? Buoyancy and BalanceSo how do we make our ROVs neutrally buoyant?Once you drill holes in your frame, your ROV will be negatively buoyant
11 BuoyancyBallastDynamic (soft): system that changes the amount of water displace inside the ballast chamber. (Think submarines)Static: ballast chamber does not change. ROV is designed to be neutrally buoyant and motors move it up and down. The volume of air stays the same.
12 What are some pros and cons to different materials? BuoyancyWhat types of materials could you use to make your ROV neutrally buoyant?What are some pros and cons to different materials?AND LOTS MORE!
13 Think about how you place buoyant materials Buoyancy and BalanceWhat about balance?Build an ROV Interactive:Knowing the center of mass for a car, for example, is enough to estimate whether it can be tipped over by maneuverson level ground. The center of mass of a boat must be low enough for the boat to bestable. Any propulsive force on a space craft must be directed towards the center ofmass in order to not induce rotations. Tracking the trajectory of the center of mass ofan exploding plane can determine whether or not it was hit by a massive object. Anyrotating piece of machinery must have its center of mass on the axis of rotation if itis not to cause much vibration.Think about how you place buoyant materials
14 Buoyancy – going further *NOTE* Totally optionalIf your students are grasping the concepts of buoyancy – you can push them further by introducing some basic calculations.
15 Buoyancy – going further PVC Pipe specifications Diameter (cm)3.3404.2164.8266.033Weight in Air(g/cm)2.5326.3577.17410.000Volume percm (cc)8.76213.96018.29228.581Net Buoyancy (g/cm) [weight in air per cm – Volume per cm]-6.230-7.603Essentially, this figure gives us the “float” value of each cm of PVCCalculations provided by the MATE center
16 Buoyancy – going further Then, weigh your ROV!Fnet (apparent weight or wet weight) of ROV = ____________g
17 Buoyancy – going further If your ROV weighs 645 g, then you will need-645g of positive, buoyant force!How many cm of 2’’ PVC pipe would you need?~ cm*You’d probably also want to add in the weight of the 2’’ PVC endcaps to the weight of your ROV before you did the calculation.
18 Buoyancy and Balance Buoyancy Let’s make these items positively, neutrally, and negatively buoyant and balanced!