VIEWS: 29 PAGES: 3 POSTED ON: 12/19/2011
Forces: 14 - 16 days Subject / Course: Physics Physics- Vectors and Forces Stage 1 – Desired Results Established Goals: (1) The student, for at least 40% of instructional time, conducts field and laboratory investigations using safe, environmentally appropriate, and ethical practices. (2) The student uses a systematic approach to answer scientific laboratory and field investigative questions (A-L). (3) The student uses critical thinking and scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to: (B) Express and interpret relationships symbolically in accordance with accepted theories to make predictions and solve problems mathematically, including problems requiring proportional reasoning and graphical vector addition. (4) The student knows the laws governing motion. The student is expected to: (A) generate and interpret graphs and charts describing different types of motion, including the use of real-time technology such as motion detectors or photogates; (B) describe and analyze motion in one dimension using equations with the concepts of distance, displacement, speed, average velocity, instantaneous velocity, and acceleration (D) calculate the effect of forces on objects, including the law of inertia, the relationship between force and acceleration, and the nature of force pairs between objects; (E) develop and interpret free-body force diagrams; and (F) identify and describe motion relative to different frames of reference. (5) Science concepts. The student knows the nature of forces in the physical world. The student is expected to: (A) research and describe the historical development of the concepts of gravitational, electromagnetic, weak nuclear, and strong nuclear forces; (B) describe and calculate how the magnitude of the gravitational force between two objects depends on their masses and the distance between their centers; Enduring Understandings: Essential Questions: Students will understand that… What is the source of forces? an unbalanced force results in acceleration. What is the relationship between forces and forces are the results of interactions. motion? inertia is a property of matter. What variables can you manipulate to affect the movement of objects? Students will know… Students will be able to… force is a vector quantity. graphically add vectors. force is measured in units of Newtons. graphically resolve vectors into components. 1 N = 1 kg*m/s2 add 2 vectors quantitatively which are either net force is the vector sum of the forces parallel or perpendicular to each other. forces are interactions between particles (an identify force pairs. agent and an object). draw and evaluate free body diagrams. forces can take the form of physical contact calculate the weight (Fg) of an object when given forces or field forces acting at a distance. a mass. examples of contact and field forces. calculate the mass of an object when given a vectors are graphically added head to tail. weight (Fg). weight is the force the earth exerts on an object’s determine the magnitude of the gravitational and mass and is dependent on the gravitational field. frictional forces acting on an object. mass is a scalar quantity based on how much use Newton’s laws of motion to solve constant matter is present and is independent of the velocity and accelerated motion problems. gravitational field. analyze and solve problems involving force forces always come in pairs which are equal in vector notation. magnitude but opposite in direction and act use Fnet=ma to solve constant velocity and simultaneously. accelerated motion problems. Revision Date: 9/3/10 mass is directly proportional to inertia. analyze and solve problems using kinematic the amount by which the forces acting on an equations and Fnet=ma. object are unbalanced is called the net force. use Newton’s Law to qualitatively describe the if more than one force acts on an object along a relationship between m and a, F and a, m and F. straight line, then the forces will reinforce or (Ie: if you double the mass, the acceleration will cancel one another, depending upon their change by a factor of …?) direction and magnitude. calculate the change in momentum of an object or the acceleration of an object is directly the impulse acting on an object given either F and proportional to the sum of the forces acting on it t or m and v. and inversely proportional to its mass (Fnet = ma) distinguish between force and impulse. unbalanced forces will cause changes in motion Solve problems involving the impulse on an including stopping, starting or changing direction. object, the forces acting on it, and the time in when forces are balanced an object will continue which they act. to move at a constant speed in a straight line or determine the force acting on an object, given remain at rest. the time the force is acting on the object, the acceleration is in the direction of the net force. object’s mass and change of velocity. motion does not require a force and the presence convert Ns into kgm/s. of a force does not always results in motion. give real life examples of how force and time frictional forces always oppose motion and interact to change the momentum of an object. depend upon the normal force and the type of explain why a greater impulse acts on an object surface. that bounces during a collision as opposed to an an unbalance force on an object produces a object that simply comes to a stop, and explain change in its momentum. what effect this extra impulse has on the object. impulse is the average force applied to an object multiplied by the time during which the force acts. impulse is a vector quantity and understand the role of positive and negative values. the units for impulse are Ns the change in momentum of an object is proportional to the force that acts on it and the length of time it acts. the area under the curve of a force versus time graph is the impulse exerted on an object. Student Preconceptions Forces are required for motion with constant velocity. Inertia deals with the state of motion (at rest or in motion) All objects can be moved with equal ease in the absence of gravity. All objects eventually stop moving when the force is removed. Inertia is the force that keeps objects in motion. If two objects are both at rest, they have the same amount of inertia. Action-reaction forces act on the same body. There is no connection between Newton’s Laws and kinematics. The product of mass and acceleration, ma, is a force. Friction can’t act in the direction of motion. The normal force on an object is equal to the weight of the object by the 3 rd law. The normal force on an object always equals the weight of the object. Equilibrium means that all the forces on an object are equal. Equilibrium is a consequence of the 3rd law. Only animate things (people, animals) exert forces; passive ones (tables, floors) do not exert forces. Once an object is moving, heavier objects push more than lighter ones. Newton’s 3rd law can be overcome by motion (such as by a jerking motion). A force applied by, say a hand, still acts on an object after the object leaves the hand. Momentum is the same as force. Moving masses in the absence of gravity do not have momentum. Revision Date: 9/3/10 Spiraling Displacement Kinematic calculations (v, x, x, a, and t) Graphing x vs t, v vs t, and a vs t graphs Motion maps Momentum Revision Date: 9/3/10