EDEXCEL IGCSE PHYSICS 1-3 Forces and Movement Edexcel IGCSE Physics pages 23 to 33 July 20 th 2011 All content applies for Triple & Double Science

Edexcel IGCSE Specification Section 1: Forces and motion c) Forces, movement, shape and momentum recall and use the relationship: force = mass × acceleration F = m × a recall and use the relationship: weight = mass × g W = m × g describe the forces acting on falling objects and explain why falling objects reach a terminal velocity describe the factors affecting vehicle stopping distance including speed, mass, road condition and reaction time

Force mass and acceleration The force, mass and acceleration of an object are related by the equation: force = mass × acceleration F = m x aF = m x a force is measured in N mass is measured in kg acceleration is measured in m/s 2

also: acceleration = and: mass = ma F force mass force acceleration

Checking the equation

Question 1 Calculate the force required to cause a car of mass 1200 kg to accelerate by 5 m/s 2. F = m x aF = m x a = 1200 kg x 5 m/s 2 Force = 6000 N

Question 2 Calculate the acceleration produced by a force of 200N on a mass of 4kg. F = m x aF = m x a becomes: a = F ÷ m = 200N ÷ 4kg acceleration = 50 m/s 2

Question 3 Calculate the force that accelerates a mass of 300kg from rest to 6 m/s over a time of 3 seconds. acceleration = change in velocity ÷ time = (6 – 0)m/s ÷ 3s acceleration = 2 m/s 2 F = m x aF = m x a = 300kg x 2 m/s 2 force = 600N

Answers Fma 24 N4 kg6 m/s N40 kg5 m/s N30 kg20 m/s 2 2 N5 g400 m/s 2 5 N100 g50 cm/s 2 24 N 40 kg 20 2 N 5000 Complete:

Car forces When a vehicle travels at a steady speed the frictional forces balance the driving force. To slow the car the engine force is reduced by releasing the throttle and the frictional force is increased by applying the brakes.

Stopping a car The total distance required to stop a car, the stopping distance, is equal to the thinking distance plus the braking distance.

Factors affecting stopping distance 1. The reaction time of the driver This will increase if the driver is tired, distracted or has consumed alcohol or drugs. Increasing reaction time increases the thinking distance. 2. The speed of the car The greater the speed the greater will be both the thinking and braking distances. Doubling the speed increases the overall stopping distance by about four times.

3. The mass of the car and its contents The greater the mass the greater will be the braking distance. 4. The condition of the road Wet and icy roads will cause the braking distance to increase. 5. The condition of the vehicle Worn brakes or worn tyres will both increase the braking distance.

Choose appropriate words to fill in the gaps below: When a car is moving at a _______ speed the engine force is equal to the resistive force. The __________ distance of a car is equal to the thinking distance plus the _________ distance. Tiredness, ________ and drugs are all likely to increase the __________ distance. A car travelling at 60 m.p.h. will require roughly ______ times stopping __________ of a car travelling at 30 m.p.h.. alcoholfourdistancesteadystoppingthinking WORD SELECTION: braking alcohol four distance steady stopping thinking braking

Mass and weight Mass is the amount of matter in an object. Mass is measured in kilograms. The mass of an object is the same on the Moon as on the Earth. Weight is the force of gravity on an object. Weight is measured in newtons. The weight of an object on the Moon is about one sixth that on the Earth. A newtonmeter is used to determine the weight of the parcel

The acceleration due to gravity (g) The acceleration due to gravity (g) varies with planet, moon and star and depends on the height of an object. Some examples of the acceleration due to gravity: Locationm/s 2 Locationm/s 2 Earth10Jupiter24 Moon1.6Pluto0.7 Mars3.7The Sun270

Gravitational field strength (g) This is an alternative way of measuring the strength of gravity. The gravitational field strength is equal to the gravitational force exerted per kilogram. Near the Earth’s surface, g = 10 N/kg In most cases gravitational field strength in N/kg is numerically equal to the acceleration due to gravity in m/s 2, hence they both use the same symbol ‘g’.

Calculating weight weight = mass × gravitational acceleration W = m x g weight is measured in N mass is measured in kg gravitational acceleration is measured in m/s 2 On the Earth’s surface a mass of 1kg has a weight of 10N.

Falling objects When an object falls through air or some other fluid initially the only significant force acting on it is the downward pull of gravity. On Earth, it will initially accelerate downwards at 10 m/s 2.

As the object speeds up frictional forces such as air resistance become greater the faster the object moves. Eventually the resultant force on the object will be zero when the frictional forces equal the weight of the object. The object then moves at a constant speed called terminal velocity.

Velocity-time graphs for a falling object

Parachuting A parachutist will have two different terminal velocities. Before opening the parachute it is about 60 m/s (140 m.p.h..). Afterwards, due the much greater drag force, the terminal velocity is about 5 m/s (12 m.p.h.)

velocity time first terminal velocity initial acceleration = 10 m/s 2 Velocity-time graph of a parachutist second terminal velocity parachute opened ground reached

Choose appropriate words to fill in the gaps below: Weight is the ______ of gravity on an object. Weight is equal to the _______ of an object in kilograms multiplied by the acceleration due to ________. Near the Earth’s surface a mass of one kilogram weighs _____newtons. When an object falls through a fluid it initially _________ because of gravity. As its ________ increases so do the frictional forces. Eventually the frictional forces are _____ to the weight of the object. At this stage the _________ force on the object is zero and the object falls with its _______ velocity. accelerates ten equal speed force mass resultant WORD SELECTION: gravityterminal accelerates ten equal speed force mass resultant gravity terminal

Online Simulations Effect of forces on motion using a space moduleEffect of forces on motion using a space module - Freezeray.com Forces in 1 DimensionForces in 1 Dimension - PhET - Explore the forces at work when you try to push a filing cabinet. Create an applied force and see the resulting friction force and total force acting on the cabinet. Charts show the forces, position, velocity, and acceleration vs. time. View a Free Body Diagram of all the forces (including gravitational and normal forces). Motion produced by a forceMotion produced by a force - linear & circular cases - netfirms Table Cloth & Other Newton 1st Law DemosTable Cloth & Other Newton 1st Law Demos - 'Whys Guy' Video Clip (3 mins) (1st of 2 clips) Inertia of a lead brick & Circular motion of a water glass Inertia of a lead brick & Circular motion of a water glass - 'Whys Guy' Video Clip (3 mins) (2nd of 2 clips) Air TrackAir Track - Explore Science Force on a Wing Force on a Wing - Explore Science Newton's 2nd Law ExperimentNewton's 2nd Law Experiment – Fendt Reaction time stopping a carReaction time stopping a car - also plots velocity/time graph - NTNU Simple gravity varying with distance and massSimple gravity varying with distance and mass - Freezeway.com Free-fall Lab Free-fall Lab - Explore Science Galileo Time of Fall DemonstrationGalileo Time of Fall Demonstration - 'Whys Guy' Video Clip (3 mins) - Time of fall independent of mass - Leads slug and feather with and without air resistance. (1st of 2 clips) Distance Proportional to Time of Fall Squared Demonstration Distance Proportional to Time of Fall Squared Demonstration - 'Whys Guy' Video Clip (3:30 mins) - Falling distance prortional to the time of fall squared. (2nd of 2 clips some microphone problems) Lunar LanderLunar Lander - PhET - Can you avoid the boulder field and land safely, just before your fuel runs out, as Neil Armstrong did in 1969? Our version of this classic video game accurately simulates the real motion of the lunar lander with the correct mass, thrust, fuel consumption rate, and lunar gravity. The real lunar lander is very hard to control. Moonlander Moonlander Use your thrusters to overcome the effects of gravity and bring the moonlander safely down to earth. BBC KS3 Bitesize Revision: Weight mass and gravity BBC AQA GCSE Bitesize Revision: Force and acceleration F=ma Stopping distances Weight Falling objects

Force and Movement Notes questions from pages 23 to 33 1.(a) State the equation relating force, acceleration and mass. (b) Calculate the acceleration that is produced by a force of 600N acting on a mass of 120kg. 2.(a) What is weight? (b) Calculate the weight of a person of mass 90kg on the surface of (i) the Earth and (ii) the Moon. 3.(a) Give two factors in each case that would increase the (i) braking distance (ii) thinking distance of a car. (b) Give one factor that if decreased would reduce both of the above. 4.Sketch and explain the shape of the velocity-time graph of a free- fall parachutist from the time of leaving a plane to the time of reaching the ground. 5.Answer the questions on pages 32 & Verify that you can do all of the items listed in the end of chapter checklist on page 32.