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- 1. 1.Introduction. Physics is the study of events in the universe and the interaction between objects. Physics is the science of nature's most fundamental and has many phenomena and natural phenomena that can be used as a basic science. Physics have often learned in junior high school and senior high school.Ever you hear about newton’s law,its like newton’s third law?Of course yes!F action= - F reaction.Its the answer that often we hear if some one answering when we asked about newton’s third law.This answer not only wrong meaning cause the answer is same with the mathematic equation.And then this argument make a misconception in this topic or material. We wont remember action reaction formula cause physics lesson isn’t just to remember step by step or like remember or memorize the song.We will introduction with newton’s law use the known concept and the aplication in our daily life.To minimalize the misconception in this material,Let’s we explain about it.
- 2. 2.Misconception in newton’s law a.action reaction force act on the same body. b.there is no connection between newton’s law and kinematics. c.the product of mass and acceleration,ma,is a force. d.friction can’t act in the direction of motion. e.the normal force on an object is equal to the weight of the object by the third law. 3.Theoritical observation. Newton’s first law Newton’s first law often we call with inertia law(kelembaman).Characteristic of weak object is the characteristic to defent condition it,that is a constant condition.if static object condition or dynamic condition.it’s like for the car that has initial condition static,will like the initial condition if we didn’t give force to it.the dynamic object with certain velocity,will move/do the motion with constant velocity without force that disturb the object.its same with newton’s first law: If all force that work at an object is equal to zero,so that an object or static object will be static,and the object that do the motion with constant velocity will do the motion with constant velocity.with mathematic,we can write: (SIGMA)F = 0 Newton's first law of motion is often stated as An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. There are two parts to this statement - one that predicts the behavior of stationary objects and the other that predicts the behavior of moving objects. The two parts are summarized in the following diagram.
- 3. The behavior of all objects can be described by saying that objects tend to "keep on doing what they're doing" (unless acted upon by an unbalanced force). If at rest, they will continue in this same state of rest. If in motion with an eastward velocity of 5 m/s, they will continue in this same state of motion (5 m/s, East). If in motion with a leftward velocity of 2 m/s, they will continue in this same state of motion (2 m/s, left). The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. All objects resist changes in their state of motion - they tend to "keep on doing what they're doing." There are many more applications of Newton's first law of motion. Several applications are listed below. Perhaps you could think about the law of inertia and provide explanations for each application. Blood rushes from your head to your feet while quickly stopping when riding on a descending elevator. The head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface. A brick is painlessly broken over the hand of a physics teacher by slamming it with a hammer. (CAUTION: do not attempt this at home!) To dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and thrusted downward at high speeds and then abruptly halted. Headrests are placed in cars to prevent whiplash injuries during rear-end collisions. While riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object that abruptly halts the motion of the skateboard.
- 4. Newton’s second law Newton’s second law will explain about condition of object if force resultant that work not zero.imagine it, if you pull the object in wet floor,the object will move with a acceleration.In experiment result,if we make a change in the force like add the force so that the acceleration will be change equal with the force change. The conclusion of the experiment can be complete in newton’s second law: The acceleration of the object is equal to or pendicular with force resultant that work,and its perpendicular with the mass. In mathematic equation,we can write: (SIGMA)F=m.a (SIGMA) F=force resultant M=object mass A=acceleration In vector equation,also can write: Fx=m.ax Fy=m.ay Fz=m.az Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object. The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased. Newton's second law of motion can be formally stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. This verbal statement can be expressed in equation form as follows: a = Fnet / m
- 5. The above equation is often rearranged to a more familiar form as shown below. The net force is equated to the product of the mass times the acceleration. Fnet = m * a In this entire discussion, the emphasis has been on the net force. The acceleration is directly proportional to the net force; the net force equals mass times acceleration; the acceleration in the same direction as the net force; an acceleration is produced by a net force. The NET FORCE. It is important to remember this distinction. Do not use the value of merely "any 'ole force" in the above equation. It is the net force that is related to acceleration Newton’s third law Definition of newton’s third law: If an object working force at the second object,so that the second object working the first object force,that total of the force=receiving force but different direction. In mathematic equation,we can write: Faction=-Freaction Faction =The force that work at object Freaction=object reaction force effect action force
- 6. Some forces result from contact interactions (normal, frictional, tensional, and applied forces are examples of contact forces) and other forces are the result of action-at-a-distance interactions (gravitational, electrical, and magnetic forces). According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of motion. Formally stated, Newton's third law is: For every action, there is an equal and opposite reaction. The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs. Friction force Friction force same with normal force,this force there if the surface of two object life touch(fisic touch)direction of the friction same with touch surface and not same with motion direction.Static friction force has maximum limit,maximum value pendicular with normal force and static friction coefisien In mathematic equation,we can write: Fmax=Ms.N If: -kinetics Fk=Ms.N -static Fs=Ms.N
- 7. 4.Explanation a.Action force and reaction force work at same object Same with newton’s second law: ‘when the object giving force to the second object,the second object giving some force but different direction with first object.’ Important to remember if action force and reaction force work at different object. For the example: a.if our hand pull the table(the force vector direction to right down),the table will pull you back too(this vector painted with different direction) b.if we walk on the floor,usually our foot will pull the floor to the behind,and then the floor pull our foot to the in front of derection. b.There is no connection between newton’s law and kinematics. In newton’s law application same with kinematics.we often find the problems that connecting between newton’s law with kinematics.because in the application of newton’s law we also explain about the acceleration,distance,and velocity that all variable inside of kinematics. For example: A car with mass 10.000 kg,move with velocity 20m/s.The car will be stop after the distance 200m.the force of car at the car stop is? Solution M=10.000kg V0=0m/s V=20m/s
- 8. F? F=m.a V2=v02+2.a.x A=0-40/(2.200) =-1m/s2 F=m.a =10.000.(-1) =-10.000 N(different direction with the force) c.the product of mass and acceleration,ma,is a force. This is false argument because product of mass and acceleration,ma.its not a force,but the perfect answer is resultant force. In mathematic equation: F=m.a For the example at an object work the force
- 9. So that F=m.a F-Ff=m.a d.Friction cant act in the direction of motion Direction of friction same with touch object surface and not same with motion direction.There are two friction force: a.static friction force b.kinetic friction force Friction force between object surface that move with push object will make friction force that the direction not same with object motion direction. There are two kinds of friction force are: Static friction force(fs): Work at static object(stop) with the equation: Fs=N.Ms Kinetic friction force(fk): Work at motion object with the equation: Fk=N.Mk Value of fk<fs
- 10. e.the normal force on an object is equal to the weight of object by the newton’s third law total force at an object in static condition is zero,this argument same with newton’s third law.and then the gravitation force with down direction at object must be confidence with the up force (normal force)its force not action reaction force that same with newton’s third law.
- 11. 5.Conclusion All of newton’s law is the basic classical to describe the motion The newton’s first law(inertia law)describe about an object will be move or do the motion in static condition if the resultant of the force not work to that’s object. The newtons second law explain about object acceleration pendicular with the total force and perpendicular with mass. The newton’s third law explain about if an object working force at the second object,so that the second object working the first object force,that total of the force=receiving force but different direction. In mathematic equation,we can write: Faction=-Freaction
- 12. Reference Giancoli,douglas C.1999.”FISIKA EDISI KE LIMA”.JAKARTA:Erlangga Suryo,asep,2009.”deskripsikan spectrum gelombang elektromagnatik.”,Jakarta https//:www.physicsclassroom.com/21
- 13. CONTENT ANALYSIS IN SCHOOL PHYSICS “MISCONCEPTION IN NEWTON’S LAW” BY: ZAKIRMAN 01951/08 PHYSICS EDUCATION LECTURER:Dra.YURNETTI,M.Pd PHYSICS DEPARTMENT MATHEMATIC AND NATURAL SCIENCE FACULTY PADANG STATE UNIVERSITY

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