Purdue University



TEACHER NOTES FOR EXPLORING KINETICSIntroductionKinetics is the study of motion of the particles along with their cause (ex. forces and torques). It asks “why did the velocity change?”Learning about pendulum’s experiment: Pendulum simulation: and motion simulation: Friction simulation: Pendulum collision experiment involving force, energy, friction, momentumRelevant 2016 ICP Content StandardsStandard 2: Uniform AccelerationStandard 3: Newton’s Laws of Motion (One Dimension)Standard 4: EnergyRelevant Physics 1 StandardsStandard 2: Constant AccelerationStandard 3: ForcesStandard 4: EnergyStandard 5: Linear Momentum In One DimensionStandard 6: Simple Harmonic Oscillating SystemsIncluded Materials12 wooden blocks weighing 200 g12 wooden blocks weighing 100 g with screw eye and string12 pieces of plywood12 rulers12 protractorsStringCalculationsGiven m1=100g=0.1 kg m2=200 g=0.2 kg μk=0.5 h=10 cm=0.1 m v1top=0 m/s v2before collision=0 m/s v1after collision=0 m/s (assume m1 stops after collision) No mass change during collisionProblemv1bot=v1before collision= ? v2after collision= ? a2after collision due to friction= ? d= ? Solution(1) EnergyEtop=Ebot PEtop=KEbot m1ghtop=12m1v1bot2 v1bot=2ghtop v1bot=2(9.8m/s2)(0.1 m)=1.96m2s2=1.4 m/s (2) Momentumpbefore collision=pafter collision m1v1 before+m2v2 before=m1v1 after+m2v2 after m1v1 before+0 kgm/s=0 kgm/s+m2v2 after v2 after=m1v1 beforem2 v2 after=(0.1 kg)(1.4 m/s)(0.2 kg)=(12)(1.4 m/s)=0.7 m/s (3) ForceFnet=m2a2=-Ffk m2a2=-μkFn since Ffk=μkFn m2a2=-μkm2g since Fn=m2g in this case a2=-μkg a2=-μkg=-0.59.8 m/s2=-4.9 m/s2 (4) Kinematicsvf2=vi2+2ad d=vf2-vi22a d=vf2-vi22a=0 m/s2-0.7 m/s22(-4.9 m/s2)=0.499.8 m=120m=0.05 m=5 cm (5) WorkDeriving and equation for d based on m1, m2, h, and μkWork is done by the non-conservative force of frictionW=Ffkdcosθbetween W= Ffkdcos180° W=-Ffkd since cos180°=-1 W=-μkFnd since Ffk=μkFn W=-μkm2gd since Fn=m2g in this case -KEafter collision=-μkm2gd since W=?KE=0 J-KEafter collision=-KEafter collision Note: KE may be lost during the collision (inelastic) so we use the KE after the collision for Work12m2v2 after2=μkm2gd 12v2 after2=μkgd since m2 is on both sides 12m1v1 beforem22 =μkgd since v2 after=m1v1 beforem2 12m12ghtopm22 =μkgd since v1bot=2ghtop and v1bot=v1before collision 12m1m222ghtop2 =μkgd 12m1m222ghtop =μkgd m1m22htop =μkd since g is on both sides and 12*2=1 d=m1m22htopμk d=m1m22htopμk=0.1 kg0.2 kg20.1 m0.5=12215m=120 m=0.05 m=5 cm (6) Graph of d vs. hd=m1m22htopμk d=m1m221μk htop + 0 y = m x + bSlope=m1m221μk 0.10.22=m1m221μk=0.1 kg0.2 kg2 10.5=1421=24=12=0.5 If m1>m2, then the slope increased (block 2 goes farther since d increases)If μk goes down, then the slope is increased (block 2 goes farther since d increases)Note: From trig, height h can be related to angle θ and length L h=L-Lcosθ%error=#theoretical-#experimental#theoretical×100% %error=0.5 - 0.45330.5×100%=9.34% EXPERIMENT: EXPLORING KINETICSIntroductionIn this lab, you will analyze the energy of a pendulum collision. Recall the following:Force is any interaction that, when unopposed, will change the motion of an object.F=ma Ffk=μkFn Fg=mgMomentum refers to the quantity of motion that an object has as a product of mass and velocity.p=mvEnergy is the ability to do work or to cause change. It is a property which can be transferred or converted into different forms commonly measured in the SI unit Joules (J)Mechanical Energy (Emec.) is the sum of an object’s potential energy and kinetic energy. It is associated with the motion and position of everyday objects.Mechanical Energy Emec.=PE+KEPotential Energy is energy that is stored as a result of position or state. Gravitational Potential Energy depends upon an object’s mass m, height h, and gravity g. This type of potential energy increases when an object is raised to a higher level.Gravitational Potential Energy PEgrav.=mghKinetic Energy is energy of motion such as an object with mass m moving at velocity v.Kinetic Energy KE=12mv2 Work is a mechanism of energy transfer.W=Fd cosθbetween HypothesisHow far will a 200g block travel with a coefficient of kinetic friction of 0.5 after being hit by a 100g block on a pendulum dropped from a height of 10 cm? How will the height h affect the distance d?Experiment DesignMaterials1-m stringPiece of plywood100 g block with metal screw eye200 g blockRulerTape or ring standProcedureMake a pendulum by tying the piece of string to the metal screw eye. Hang the pendulum over the edge of a desk or on a ring stand so that the block just clears the top of the plywood placed on a level surface beneath it. Tape the upper end of the string if needed.Place the 200g block on the plywood so that it will collide with the 100 g block when the pendulum string is vertical. Let the 100 g block hang in place next to the 200 g block to make sure the collision will happen properly.Pull the bob up and to the side until it increases its height by 5 cm, 10 cm, 15 cm, and 20 cm. Release the block for each height three times and take the average. Record the data in the table below. You can discard a trial if you have a good reason to do so (ex. block hits plywood instead of other block).DataHeight of 100g Wood Block (cm)Distance 200g Wood Block Moved (cm)Trial #1Trial #2Trial #3Average05101520AnalysisGraph your distance vs. height (you can use graphing software like excel or sheets as well)136588571755Dependent variable vs. Independent variable (by convention)00Dependent variable vs. Independent variable (by convention)right1972310Responding (Dependent) variable00Responding (Dependent) variable-70870-39763706510544427186690010795Manipulated (Independent) variable00Manipulated (Independent) variableBased on your data, how did the impact height affect the distance?What are some sources of error?ConclusionWas your hypothesis correct? Explain.When does a swinging pendulum have the most kinetic energy?Where did the pendulum get its kinetic energy?Was there energy lost in the collision? What can we assume was conserved?Why did the 200 g wooden block stop? ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download