9.1 Ideas of DENSITY Learning objectives: - Define mass, pressure and density - Explain if an object will float or sink depending on its density - Explain why solids, liquids and gasses have a different density Why these object/substances can arrange themselves in different layers? What do you notice? What is the same and what is different? Which one is heavier? What is MASS? What do you notice? What is the same and what is different? Which one is heavier? What is VOLUME? So, what are the physical quantities that could affect density? What is DENSITY? PRATICAL – Comparing materials Put them in order of density from the lightest to the heavier then write your observations in the book Use the material and metal box kit Can you match each substance with the right density? DENSITY 0.94 11.3 0.93 0.85 0.79 19.3 2.7 1.0 0.0013 What is denser? A solid a liquid or a gas? Why 9.2 Measuring DENSITY Learning objectives: - Use the formula of density in reallife situations - Describe how to measure the density of a regular object - Describe how to measure the density of a irregular object What is their density? Their mass is 10 Kg and 1 kg Which one is heavier? PRATICAL 1 – Measuring the density of different materials Each group use some of the regular blocks in the metal and material box kit to measure the density of different materials How can we measure the density of an irregular objet? PRATICAL 2 – Measuring the density of different materials Use a digital scale and a measuring cylinder to calculate the density of different objects. Then write the full method and calculations 9.3 DENSITY calculations Learning objectives: - Use the formula of density tp solve mathematical problems - Describe how to measure the density of a gas Complete the following working sheet 0.8 m 0.8 m 0.2 m 0.8 m 0.2 m A wooden cube has a mass of 307.2 g and a density of 0.6 g/cm3. Find the length of the cube A butter block weights 200 g and has a density of 0.83 g/cm^3. Calculate the volume. 0.2 m 2400 x 0.768= 1843.2 kg 11.5 x (5x5x3) = 862.5 862.5 g = 0.8625 Kg 19 (3.14 x 3^2) = 536.94 0.384 0.256 0.128 A wooden cube has a mass of 307.2 g and a density of 0.6 g/cm3. Find the length of the cube 25 / 2 = 50 11.5 x 40 = 460 g 307.2 /0.6 = 512 512 = 8 cm A butter block weights 200 g and has a density of 0.83 g/cm^3. Calculate the volume. 200 / 0.83 = 240.96 1000 / 200 = 5 8.5 / 588 = 4998 g = 5 Kg DEMO – Activity 9.3 Measuring the density of a gas (air) 9.4 Pressure 9.5 Pressure calculations Learning objectives: - Explain what is pressure including the the factors that affects it - Solve problems about pressure What happen when you walk on a sand beach? Why do you leave footprints? What is pressure? A force that pushes on a surface DEMO: Can you penetrate the wall with a finger? Can you penetrate the wall with a pin instead? Why a drawing pin is designed with a sharp point and a broad head? What can we say about the factors that affect pressure? Surface area and force What is the formula for pressure? P = F /A What is the SI unit for pressure? P = N/m2 = Pascal (Pa) Problem: What is the pressure if N = 8 and A = 4 cm2? P = F (N)/A P = 8 N/ 4 2 m 2 (m ) =2 2 N/m Problem: which of these four stumps exert the greatest pressure? Stump A: F=20N, A=2cm2 ; p = 10 N/cm2 Stump B: F=30N, A=2.5cm2 ; p =12 N/cm2 Stump C: F=45N, A=3cm2 ; p = 15 N/cm2 Stump D: F=16N, A=1cm2 ; p = 16 N/cm2 D force is the smallest but exert the greatest pressure because concentrated in a smaller area W/S: 9L1 Pressure PRACTICAL: Who exerts the greatest pressure in the class by standing on one foot? Write your prediction, and then test it. What do you need to do? 1 Measure the area of your foot without considering the broken squares 2 Measure the mass and find the F = m x g 3 Use the formula of pressure to calculate your pressure The surface area of a one of these snow shoes is ten times the size of a foot. Why is it easier to wear those to walk in snow? Use the calculations from the previous activity to explain your answer. What F is produced if a pressure of 1000 N/m2 act on A of 200000 cm2 (20 m2 x 1000 N/m2 = 20000 N) Find A if the a F of 700 N create a pressure of 70 N/m2 (700 N / 70 N/m2 = 10 m2) W/S: 9L1 Interpreting results W/S: 9La/3 Pressure points 9.6 Pressure in gases and liquids Learning objectives: - Describe what creates pressure in a liquid - Describe how hydraulic machines work - Explain the difference in compressing a liquid or a gas - Describe what creates pressure in fluids at the molecular level DEMO 1: Tank with three holes DEMO 2: Cork in water: Why is the cork floating? Thanks to an upward force (from water) called upthrust and because it’s density is lower and water density W/S: 9L2 Pressure all around Pressure at the surface = 1 ATM What is the pressure at 50m considering that it increases by 1 ATM after every 10m? Pressure at -50 m = 6 ATM DEMO 3: Compress a bottle filled with water Is water easily compressible? What happen when pressure is applied to the liquid? The liquid will push back with the same force, pushing on the container Is the pressure the same at every point in the liquid? Yes Demo 4: Hydraulic machines (transmitting pressure via syringes) – Write your observations W/S: 9Lb/3 A question of pressure Which one has more pressure why? DEMO 5: Compress a bottle filled with air Is air more compressible than water? Why? Because air molecules are much further apart with lot of empty space in between that is easier to be compressed DEMO 6: Fill up a balloon Why is the balloon increasing in size? When pressure is applied to a gas, it pushes back with equal and opposite pressure. The pressure of the gas is created by the gas molecules as they collide with and rebound from the container W/S: 9Lb/4 Atmospheric pressure W/S: 9Lb/2 Pressure effects 9.7 The turning effect of a force Learning objectives: - State what is a laver and describe its utilisation referring to different examples - Explain the difference between a force-magnifier and a distance-magnifier - State how can you measure the weight of an object with a balance scale Moments – theimages turningare effect of a force What these showing? The external force applied allows a rotation During these actions an external force (effort) is applied. How does it affect the the movement about a fulcrum (pivot), making object to produced? turn in the direction of the force applied What is a lever? Simple machine that decreases the force needed to do a job Can you think of some examples about levers? What A longer can belever donecan to increase be used to theincrease turning the effect usingturning less force effect, in doing usingthese less force actions? Levers can be used as: • Force-magnifier: decrease the force needed for a purpose, like lifting a load • Distance-magnifier: a small movement near the pivot becomes a lager movement at the other hand, away from the pivot (hand of a clock) W/S: 9L3 Force at work What is this? How does it work? Activity 9.7 Scale maker 9.8 The principles of moments 9.9 Calculating moments Learning objectives: - State what is a moment - List the factors that can change it, and name its two possible directions - Solve problems using the formula for moments - Perform a practical invetigation in studying the principle of moments What is happening in this situations? How do they differ? What is a moment? Turning effect of a force What are the factors that can change a moment? Force and distance What is the formula to calculate a moment Moment = F x d What is the SI unit of moment? Nm Problem: A 25 kg boy is on a seesaw, 250 cm away form the pivot. What is its moment? F = 25Kg x 10 N/Kg = 250 N Moment = 250N x 2.5m = 625 Nm Moments in balance: Seesaw example: What is the direction of the F of these two people? Pointing downwards What it the direction of the turning forces? Clockwise and anti-clockwise Question: In a seesaw, if a heavier kid has a mass that is double of the mass of a smaller kid, what is the distance from the pivot that he should be sited, to balance the seesaw compare with that one of the smaller person? Half W/S: 9Lc/1 Investigating levers 1 W/S: 9L3 Levers Practical: Activity 9.8 Balancing a beam W/S: 9L4 Testing the principle of moments W/S: 9L4 Moments