Forces- the great rice challenge Buoyancy and gravity Buoyancy is also known as upthrust and is a force exerted by a gas (air) or liquid (water)that tries to push the object upwards, hence the name upthrust. You will need: - a large bowl to fill with water. - a piece of A4 paper - aluminium foil - scissors - a tablespoon - and some plasticine or a some other object that you can use as a small weight, such as a small stone. Use an A4 piece of paper as a template and cut some aluminium foil to the same size as the A4 piece of paper. Fold the foil into the shape of a boat that will be used to carry as much rice as possible. The boat must: - be made entirely from an A4 sized piece of aluminium foil. - be stable as it is floating on the surface and not tip to one side as the water moves around it. A little plasticine can be used as ballast. Cut a small piece of plasticine and place it at the bottom of the boat. The further away the plasticine is from the bottom of the boat the more stable the boat will be. See one design shown on the right. Push the boat into the water with your finger. You will feel a force exerted by the water pushing the boat back up. This force, exerted by the water, is known as buoyancy. What do you notice about the level of the water in the container as you push the boat in the water? Now see how many tablespoons of rice can be carried by your boat at least twice round the bowl without sinking. 1) Look at the model boat, shown on the right and built by Nicholas. It is floating on the surface of the water. a) What two forces are acting on the boat to keep it floating on the surface? Gravity and drag Drag and buoyancy Buoyancy and gravity Thrust and drag b) The forces mentioned in a), above, are: unbalanced strained balanced c) The boat has a little propeller that provides a force to push it through the water. Since the boat is traveling at constant speed around the bowl which comment below is true? The forces of thrust and drag are unbalanced The forces of thrust and drag balanced There is a net force keeping the boat moving forwards. d) The boat is traveling in a circle constantly changing direction as it hits the wall. Which comment is true? balanced forces are acting on the boat to change it's direction A net force is acting on the boat to change it's direction A zero net force is acting on the boat. 2) Zach was onto a record number of tablespoons of rice when all of a sudden his boat sunk into the water. Zach was asked to explain what happened. Which comment below is correct? The forces of gravity and buoyancy became unbalanced and a net force acted on the boat pushing it into the water. The forces of gravity and drag became balanced and a net force acted on the boat pushing it into the water. The forces of thrust and buoyancy became unbalanced and a zero net force acted on the boat pushing it into the water. 3) The picture on the right shows a cargo vessel traveling on the surface of the water at constant speed and direction. Two of the forces acting on the vessel are shown with arrows and in the direction which the forces are acting. a) Name all the forces acting on the vessel. b) Draw the arrows to represent the other two forces. Indicate the size of each force by drawing an appropriately sized arrow and indicate the direction in which the force is acting. The Bermuda triangle has always being shrouded in mystery. Supernatural phenomena have being used to explain the many disappearances of cargo and military vessels from it's waters. Science may now have an answer. It has long being known that a great deal of gas deposits are found beneath the ocean floor in the Bermuda triangle. Could sudden releases of huge volumes of gas be responsible for the sinking of many vessels? View the video on the right from the BBC. 4) What is a possible hypothesis being investigated? 5) Does the evidence support the hypothesis in 4) above? 6) What does this experiment tell us about a possible explanation? BBC video sourced from https://www.youtube.com/watch?v=MSmAXp_BHcQ 17/5/2020 9.10 pm