4Weight vs. MassEarth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N.WGMWeight = Mass x Gravitational Field Strength(in N) (in kg) (in N/kg)What is the weight on Earth of a book with mass 2kg?What is the weight on Earth of an apple with mass 100g?Dave weighs 700N. What is his mass?On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon?
5Balanced and unbalanced forces ReactionConsider a camel standing on a road. What forces are acting on it?These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere.Weight
6Balanced and unbalanced forces ReactionWhat would happen if we took the road away?Weight
7Balanced and unbalanced forces What would happen if we took the road away?The camel’s weight is no longer balanced by anything, so the camel falls downwards…Weight
8Balanced and unbalanced forces 1) This animal is either ________ or moving with _____ _____…2) This animal is getting _________…3) This animal is getting _______….4) This animal is…
9Balanced and unbalanced forces Fnet=200NF=-100NF=200NFnet=100NF=-200NF=200NFnet=0NF=-200NFnet=-200N
11Gravity all bodies have gravity we feel it only from planet sized objects T=0 v=0m/sAcceleration due to gravity is 10m/s2That means every falling body gets 10m/s faster every secondT=1s v=10m/sT=2s v=20m/sT=3s v=30m/s
15More force means more Extension Force is proportional to extension Hookes LawForce1234567891011121314151617181920ExtensionMore force means more Extension Force is proportional to extension
16Hookes Law Calculation 1234567891011121314151617181920123456789101112131415161718192012345678910111213141516171819201234567891011121314151617181920Force=24NLength=17cmExt.=12cmForce=0NLength=5cmExt.=0cmForce=6NLength=8cmExt.=3cmForce=12NLength=11cmExt.=6cm
18Stopping a car… Tiredness Too much alcohol Thinking distance Too many drugsPoor visibilityWet roadsIcy roadsStopping distanceTyres/brakes worn outDriving too fast
19Work done Work done = Force x distance moved W D F When any object is moved around work will need to be done on it to get it to move (obviously).We can work out the amount of work done in moving an object using the formula:Work done = Force x distance movedin Joules in Newtons in metersWDF
20Work Done LiftingLift a mass of 80kg a height of 6m. How much work is done?Work done = Force x distance movedWork done = 800N x 6mWork done = 4800 Joules
21Power The rate at which work is done POWER = Work Done time taken Example A microlite takes 20s to climb to 100m. If the microlite has mass 2000kg find the work done and the power?Work Done = Force x Distance = 2000x10 x = JoulesPower = Work Done / Time = Joules / 20= Watts
22QuestionOn a school trip a pupil of mass 50kg climbs the Eiffel Tower. If the tower is 320m high and he takes 50mins (3000s) find his work done and power.
23Pressure F A P Pressure depends on two things: How much force is applied, andHow big (or small) the area on which this force is applied .Pressure can be calculated using the equation:FAPPressure (N/m2 or Pa) = Force (in N)Area (in m2)Pa is Pascals
24Calculating PressureTo use the triangle we have to cover the letter we do not knowF=PxAFind the force that we need to have for a pressure of 10Pa over an area of 2m2?
25Balloon Pressure ExptSpread it out share the weight man
26A circus elephant weighs 10,000N and can stand on one foot A circus elephant weighs 10,000N and can stand on one foot. This foot has an area of 0.5m2. How much pressure does he exert on the floor (in Pa)?Pressure=Force/area= 10000N/ 0. 5m2 = Pa
27A 50kg woman copies the elephant by standing on the heel of one of her high-heeled shoes. This heel has an area of 1cm2. How much pressure does she exert on the floor?Pressure=Force/area= 500N/ m2 = Pa
28Pressure – in FluidsPressure increases with depth
29As the frog goes deeper there is a greater weight of water above it. Pressure and DepthAs the frog goes deeper there is a greater weight of water above it.
30Atmospheric Pressure ATMOSPHERIC PRESSURE The earth is covered with layer of Gas.We are at the bottom of a gas ocean 200km deep.The effect of this huge column of gas is 1 Tonne of weight on our shoulders.This is calledATMOSPHERIC PRESSUREHeavy!
31The Barometer The weight of the air holds up the mercury. VacuumThe weight of the air holds up the mercury.If we use water the column is 10.4m high.1 Atmosphere is 760mm of Hg.
32The Altimeter Air is also a fluid As we go higher there is less air above us.There is less Atmospheric pressureWe can measure the altitude using a barometer with a different scale.
37Center of GravityThings stay standing (STABLE) because their Center of Gravity acts through their base.
38EquilibriumThings fall over because the center of gravity is outside the base
39EquilibriumThere are 3 types of equilibriumSTABLENEUTRALUNSTABLE
40Center of GravityThe place where all the mass of the body appears to act.How do we find the center of gravity of this flat piece of card?
41of the body appears to act Center of Gravity of a Lamina We must freely suspend the lamina from three places Then we trace the plumb line onto the paper.Center of GravityWhere all the massof the body appears to act