2 Learning Objectives Can define what a force is Can explain Newtons 3 laws of motionUnderstand the 3 types of motionCan place this information into a variety of sporting examples
3 Success Criteria Can define Force Can recall Newtons 3 laws with examplesCan place the types of motion into examples
4 WHAT IS A FORCE?With a partner 30 seconds discuss
5 FORCE isA push or pull that alters, or tends to alter, the state of motion of a bodyThe force applied to the trampoline to allow the downward phase of a jump to change to the upward phase of the next jumpOn mini whiteboard give an example and show me
6 1995?This is a perfect example of when everything came together within a sporting context.It shows ultimate knowledge, control andexecution of internal and external forces tobreak the World Record.A distance that still stands since 1995
7 Jonathan Edwards http://www.youtube.com/watch?v=dFt9Yzp484c
8 FORCE FORCE is push or pull the unit is the NEWTON (10 N is approx the weight of 1 kg)force changes the state of motion of an objectforce causes acceleration or deceleration or change of directionthe more force the bigger the accelerationforce changes the shape of an objectWEIGHT, FRICTION, REACTION FORCES, AIR RESISTANCE / FLUID FRICTIONall these forces affect the sportsperson
10 Newton’s First Law - INERTIA An object will continue in a state of restor uniform motion unless acted upon byan external force.If an unbalanced force acts on an object, it will accelerate in the direction of the unbalanced force.If an object is given a certain initial velocity and there are no unbalanced forces acting on it, the object will continue along its original path in a straight line.
11 INERTIAGive 3 examples from sport where you may see this law in practise:1.2.3.Staying in the blocks in a 100m sprintA cricket ball will keep travelling after being hit for a 6The High Jumper will keep going up over the barWhere is the only location where inertia cannot be influenced?In space inertia cannot be influenced by external factors therefore on Earth everything can be influenced. The sprinter will not stay in the blocks for ever and the ball will fall and the higher jumper won’t always clear a height...why?
12 Newton’s Second Law - Acceleration When a force acts on an object, theobject is accelerated by an amountdirectly proportional to the forceapplied and inversely proportionalto the mass of the object(F = ma) force = mass x accelerationThe greater the force being exerted on an object, the faster the object moves.The greater the mass of the object, theslower the object will move in relation to a lighter object with the same force applied. A big mass (tennis ball) is harder to accelerate than a smaller mass (table tennis ball).Simply: 10N force against a tennis ball or a shot putt which travels furthest
13 Newton’s Second Law - Hockey If a player strikes the ball, its accelerationis determined by the mass of the balland how hard the player hits it (F = ma).If the ball were heavier (larger mass), it would accelerate less.If the player hits the ball harder (larger force), the ball accelerates more quickly.FMA
14 Newton’s Second Law - Baseball A baseball player on deck getting ready to bat adds weights to their bat to practice swinging, and to warm up their muscles. If the total mass of the weights added is equal to the initial mass of the bat, then the weight is doubled. If the batter swings at a constant speed (a), and applies a uniform force throughout (F), we can apply Newton’s Second Law.When he removes the weights, the mass is cut in half, and the acceleration will be twice as fast as before. A batter gets an advantage if he uses Newton’s Second Law before stepping onto the plate.
15 Newton’s Second Law - Baseball Q1. A batter swings with 200N of force on deck circle, with weights attached making the bat twice as heavy as usual. What is the bat’s acceleration: a) on the on deck circle? b) at the plate when the weights have been removed? Q2. A bat has an acceleration of 80m/s2. What force was applied to the bat? Q3. A batter at the plate swings with a force of 100N. What is the bat’s acceleration? How does this compare to the answer to Q1.b?Note: A bat has a mass of 2 kg.
16 Newton’s Second Law - Baseball A1. a) F = ma b) F = ma a = F/m a = F/m a = 200N/4kg a = 200N/2kg a = 50m/s2 a = 100m/s2 A2. F = ma F = 2kg x 80m/s2 F = 160N A3. F = ma The force applied is a = F/m half that in Q1.b, a = 100N/2kg therefore, the a = 50m/s2 acceleration is halved.
17 Newton’s Third Law - Reaction “For every action there is an equaland opposite reaction”For every force between two objects there is always an equal but oppositely directed force.The normal reaction force isthe support force exerted uponan object which is in contactwith another stable object.Question:When hitting a baseball, if we call the force on the bat against the ball the action force, what is the reaction force?Normal reaction forceWeight
18 The reaction force is the force exerted by the ball on the bat. Newton’s Third LawWhen a swimmer turns, the pool wall pushes against the swimmer with the same force as the swimmer pushes against the pool wall.When a weightlifter pushes against the ground, the ground pushes against the weightlifter with the same force.When a tennis player hits a ball with their racquet, the tennis ball exerts an equal but opposite force on the player’s racquet.Can you think of any more examples?Answer:The reaction force is the force exerted by the ball on the bat.
19 Newton’s Third Law - Hockey For every force exerted by an object, an equal and opposite force is exerted on the object.
20 Homework Sentence Summary: Write a series of sentences to summarise Newton’s Laws.Give examples of two Olympic sports you can show Newton’s Laws working.Write an equation for the 2nd law
21 Success Criteria Can define Force Can recall Newtons 3 laws with examplesCan place the types of motion into examples
23 MOTION Motion is movement and is divided into 3 main categories: LINEAR MOTIONGENERAL MOTIONANGULAR MOTION
24 LINEAR MOTIONWhen a body moves in a straight or curved line with its parts moving the same distance in the same direction at the same speedE.g.. A tobogganistShot put ( curved line with no spin imparted at release)What else?......Show me......Linear motion occurs when a force is applied through the centre of mass of the body/object
25 ANGULAR MOTIONWhen a body or part of a body moves in a circle or part of a circle about a particular point called the axis of rotation.-Bicycle wheel-Movement around our joints (fixed points)-Front crawl in swimming (ARMS)-The high bar in men’s Olympic gymnastics
26 GENERAL MOTION A combination of linear and angular motion Javelin throwerWheel chair athleteSprinterSwimmerThis is by far the most common motion type inSport
27 Examples of motion in sport Linear:Angular:General:
28 TASKIN GROUPS USING AS MANY DIFFERENT SPORTS AS YOU CAN THINK OF, LIST:Three examples of pure linear motionThree examples of pure angular motionThree examples of general motion
29 CENTRE OF MASSThe ‘Centre of Mass’ is where the weight of a body tends to be concentrated.This is the point at which the body is ‘balanced in all directions’Therefore in objects such a tennis balls and shotputts the c.o.m. Would be at the very core.
30 However c. o. m. can be outside the body However c.o.m. can be outside the body. In humans this is not in the same position but moves constantly as we do.A coit used in primary schools for play the c.o.m. Is in the centre, but there is nothing there
31 A prime example in sport is the high jump At this moment the c. o. m A prime example in sport is the high jump At this moment the c.o.m. is outside the body underneath the back
33 It is only really feasible in moving objects especially people and animals that the c.o.m. Is identified if the body is STABLE. Stability is important for balance, gymnastics is a good example such as the beam
34 Stability is dependent upon these factors: Position of the centre of massBase of supportPerformers line of gravityMass of the performer
35 Stability This is a stable position because…. It would become less stable by……StabilityCentre of MassBase of SupportLine of Gravity
36 Centre of Mass and Application of Force The direction of the force being applied, in relation to the centre of mass, will dictate if the motion is linear or angular.If the line of the force is through the centre of mass the resulting motion will be linear. This is called a direct force.If the line of force passes outside the centre of mass the motion will be angular.This is called an eccentric force.
37 Centre of Mass and Application of Force Ball spins – angular motion.Ball goes up but with no spin – linear motion.Liner MotionAngular MotionForce applied through centre of mass – direct force.Force applied to side of ball – eccentric force.The more spin needed the greater the force and the further away from the centre of mass it needs to be applied.