Practical 2Topic : Force and motionActivity 1: Identify different types of force in different contexts. Purpose : To identify the different types of force in different contexts.Theoreticalknowledge :A force is a push or pull acting upon an object as a result of itsinteraction with another object. There are a variety of types of forces.Previously in this lesson a variety of force types were placed into twobroad category headings on the basis of whether the force resulted fromthe contact or non!contact of the two interacting objects.Contact Forces Action-at-a-Distance ForcesFrictional Force Gravitational ForceTension Force Electrical ForceNormal Force Magnetic ForceAir Resistance ForceApplied ForceSpring ForceType of Force"and #ymbol$Description of ForceApplied ForceFappAn applied force is a force which is applied to an object by a person or another object. %f a person is pushing a desk across the room then there is applied force acting upon the object. The applied force is the force exerted on the desk by the person.&ravity Force"also known as 'eight$FgravThe force of gravity is the force with which the earth moon or other massively large object attracts another object towards itself. (y definition this is the weight of the object. All objects upon earth experience a force of gravity which is directed )downward) towards the center of the earth. The force of gravity on earth is always e*ual to the weightof the object as found by the e*uation:Fgrav = m * gwhere g + ,.- m.s/ "on 0arth$ and m + mass "in kg$"1aution: do not confuse weight with mass.$2ormal ForceFnormThe normal force is the support force exerted upon an object which is in contact with another stable object. For example if a book is resting upon a surface then the surface is exerting an upward force upon the book in order to support the weight of the book. 3n occasions a normal force is exerted hori4ontally between two objects which are in contactwith each other. For instance if a person leans against a wall the wall pushes hori4ontally on the person.Friction ForceFfrictThe friction force is the force exerted by a surface as an object moves across it or makes an effort to moveacross it. There are at least two types of friction force! sliding and static friction. Thought it is not always the cast the friction force often opposes the motion of an object. For example if a book slides across the surface of a desk then the desk exerts a friction force in the opposite direction of its motion. Friction results from the two surfaces being pressed together closely causing intermolecular attractive forces between molecules of different surfaces. As such friction depends upon the nature of the two surfaces and upon the degree to which they are pressed together. The maximum amount of friction force which a surface can exert upon an object can be calculated using the formula below:The friction force is discussed in more detail later on this page.Air 5esistance ForceFairThe air resistance is a special type of frictional force which acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object. This force will fre*uently be neglected due to its negligible magnitude "and due to the fact that it is mathematically difficult to predict its value$. %t is most noticeable for objects which travel at high speeds "e.g. a skydiver or a downhill skier$ or for objects with large surface areas. Air resistance will be discussed in more detail in 6esson 7.Tension ForceFtensThe tension force is the force which is transmitted through a string rope cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls e*ually on the objects on the opposite endsof the wire.#pring ForceFspringThe spring force is the force exerted by a compressed or stretched spring upon any object which is attached to it. An object which compresses or stretches a spring is always acted upon by a force which restores the object to its rest or e*uilibrium position. For most springs "specifically for those which are said to obey )8ooke9s 6aw)$ the magnitude of the force is directly proportional to the amount of stretch or compression of the spring.:aterials : i. A wooden blockii. A ping! pong balliii. A stretched wire on a wooden blockiv. A beakerv. A bookProcedures :;. A wooden block is placed on the floor. The wooden block has been given a push and the observation is recorded./. A ping! pong ball is thrown up into the air. The observation is recorded. 7. A piece of wire was tie tightly between / nails hammered into a piece of wood. The wire has been touched. The observation is recorded.. The inferences for each of these observations are stated like in the table below. 5esults :Procedures Oservation InferencesProcedure 1The wooden block wasmoved and then it stops.The wooden block moved because a force has been applied on the wooden block. After that it has been stop because some force such as the resistance and the gravity forces also had on the wooden block.Procedure 2 The ping! pong was goingup after being thrown andthen it drops at the sameplace it has been thrown.The ping! pong was going up because a force has been given to the ball. 'hile going up there was a resistance force that hadcontact on the ball. This had made it slow. There is also a gravity force on the ping! ping. The gravity force is higher than the other forces. This had made an unbalance force. #o the ball is fall back. Procedure !The wire was move jerkilyand then it has stop andbeing normal back.The wire was move jerkily because of the force that has been given to it. #o there will be the tension force. After several seconds it had stop because there were no force was given after that. Procedure "'hile we push the ping!pong down towards wehad fill that it is hard. Afterwe let go the ping! pong ithas been float on thesurface of the water.The ping! pong can be in the water because of the force that has been given by us. 'e had pushed it. 'hile we push the ping! pong we also had filled some force at our hand from the ball. This is because there were a force in the water which pushing our hand up. Procedure # The book is heavy.The book was heavy because there was a force that had contact with the book. #o we had tried to make the book to stay on its position. That was why we can fill that the book was heavy. 1onclusion : The inferences are accepted. This is because there were such forces that have been contact with the objects that have been used in this experiment. The force had contact on the objects by make it slow or stop float changing direction and many else. Activity 2: $easuring t%e acceleration of a freely falling o&ect.Purpose : To measure the acceleration of a freely falling object.Theoreticalknowledge :#ystematic experiments on freely falling objects and objectsmoving on inclined planes were carried out by 'alileo 'alilei";=>7>- km.%f you climb a ;??? m high mountain your distance from thecenter of theearthchangesby";.>7>-$@;??A+?.?;>Aandthemagnitude of the acceleration vector changes by ";.>7>-$/@;?? A + /. A.For all objects near the surface of the earth the distance fromthecenter isnearlyconstant andthemagnitudeof thegravitationalacceleration vector is therefore approximately constant.'e denote thegravitational acceleration vector by g.%ts magnitude is g + ,.- m.s/ anditsdirectionisstraight downward. 3ver small distances whenthecurvature of the earth9s surface can be neglected the direction of thegravitational acceleration vector is also nearly constant. 2ear the surface of the earth g is the same for allobjects.Allobjects accelerate at approximately the same rate. Freely fallingobjects are therefore objects which are moving with constantacceleration g.Fromother resources it says thatafree!fallingobject isanobject whichisfallingunderthesoleinfluenceof gravity. Anyobjectwhich is being acted upon only be the force of gravity is said to be in astate of free fall. There are two important motion characteristics whichare true of free!falling objects: Free!falling objects do not encounter air resistance. All free!fallingobjects"on0arth$acceleratedownwardsat arateof ,.-m.s.s"oftenapproximatedas;?m.s.sforback-of-the-envelope calculations$(ecause free!falling objects are acceleratingdownwards at a rate of ,.- m.s.s a ticker tape trace or dotdiagram of its motion woulddepictacceleration. The dotdiagramat theright depictstheaccelerationof afree!fallingobject. Thepositionof theobject at regular timeintervals ! say every ?.; second ! is shown. The fact thatthe distance which the object travels every interval of timeis increasing is a sure sign that the ball is speeding up as itfallsdownward. 5ecall fromanearlierlesson that if anobject travels downward and speeds up then itsacceleration is downward.Free!fallacceleration is often witnessed in a physics classroomby means of an ever!popular strobe light demonstration. The room isdarkened and a jug full of water is connected by a tube to a medicinedropper. The dropper drips water and the strobe illuminates the fallingdropletsat aregular rate! sayonceevery?./seconds. %nsteadofseeing a stream of water free!falling from the medicine dropper severalconsecutivedropswithincreasingseparationdistanceareseen. Thepattern of drops resembles the dot diagram shown in the graphic at theright:aterials: i. A ticker! timerii. Ticker tape iii. 1lamp iv. Power packv. 1onnecting wiresvi. :asses of 7??g ??gvii. 1ello tapeProcedures : ;. A chair is placed on top of a table. A ticker! timer was clamp onto theupper side of the chair. /. A piece of ticker tape is fixed through the ticker! timer and then a 7??g mass was cellotape to the tape.7. The ticker! timer was switch on and the mass was let to fall freely downwards.. A graph for each case was build from their strips and then was determined their acceleration.Diagram of experiment5esults : $ass (g) Acceleration (ms*2)7?? ,.=?? ;;.>1onclusion : As the conclusion my friend and % have found out that every object in this world have the same mass. %t also has the same acceleration while it is freely falling. This is becauseB the gravity on 0arth is same at any places although the object has different mass. Ciscussion : ;. %n activity ; we have done the experiment for identify the different types of force in different contexts./. There were several types of forces such as tension thrust normal weight and friction. 7. All of these forces always happen in our daily life. #o % had prepared the table to list the forces that happen for each procedure.+iagrams +escription of forces in t%e diagram1. (efore the wooden block moved it was in balanced force. This is because there were the normal and weight force that were contact with the wooden block. #o it staid in it position.'hile we pushed the wooden block we had given it a force. #o it has moved. There are also2.A force that was contact with it which is the resistance. The resistance was made by the floor. #o it will make it stop after several seconds. After it stops there were several forces that contact on it which are the friction force normal force and weight force.!. 'hile we touch the wire there was a force that contact on it. %t is the tension force. %t has made it stretched firmly. #o the wire has moved jerkily because of the force. ". There was a surface tension on the water in the beaker. %t has made the ping! pong being on the surface.'hile we pushing the ping! pong ball into the water we have gave a force on the ping! pong so that it will be in the water.'e can fill some force that pushing on our hand.This is because of the force in the water which isadhesion and cohesion. After we let go the ping! pong the ball will come up to the surface. This is because of the force that contact on it. The force is thrust force. #. 'e can fill the heavy of the book because of the force that contact on it. The force is weight. %t happens because of the gravity.'hile the book is on our hand we also have given a force on it which is the normal force to maintain the position of the book. #o there was balanced force.