PHY 103 2nd EditionExam # 2 Study Guide Lectures: 7-18Lecture 7 (September 24)Dynamics- ForcesHow do you determine Net Force? What does it mean for an object to be in equilibrium? Net Force is determined by using vector addition. We must remember that vector addition can only happen along the same plane, therefore we may be required to break a force into its component vectors in order to add them. An object in equilibrium means the forces acting on the object are balanced and there is zero acceleration. This does not mean that the object cannot be in motion.What is Newton’s First and Second Law?Newton’s First Law states that objects at rest remain at rest and objects in motion remain in motion (at a constant velocity) unless acted on by a force. This is also called inertia. Inertia is closely related to mass in that objects with greater mass have larger inertia than objects with lesser mass.Lecture 8 (September 26) Dynamics (continued)What is the difference between mass and weight? Mass is a measure of inertia, while weight is a measure of the force of gravity on an object closeto the earth’s surface. Weight is given by the equation W = Fgravity = magravity = -mgŷ.What is Newton’s Third Law? What do we look at in this law?Newton’s Third Law states that every force has an associated force with equal magnitude but opposite direction. Careful! This does not mean that motion is impossible. This law examines a force and its reaction, which occur on different objects, thus allowing and explaining motion.How do we deal with systems that have multiple masses?We must be careful to differentiate between external and internal forces. External forces often occur on only one mass, but then can indirectly be applied to the other masses. External forces also contribute to net force. Internal forces on the other hand, act within the system, therefore they do not appear in the system’s equation for net force. An example of this would be tension.Fpull T12 T21In this example, the two objects are connected by a string, therefore, they would have an equalacceleration. This acceleration wouldcome from the Fpull on the first block. The tension is in the string connecting the blocks and would cancel each other out because they are equal and opposite.Lecture 9 (September 29)Dynamics (continued)What is a free body diagram? How do we use them?A free body diagram is a picture drawn to show all of the forces acting on an object or a system. The object or system is depicted by a point. Then force vectors are drawn, acting on that point. We use these diagrams to simplify ideas and to help keep track of all the forces. m1: Ftension1 m2: Ftension2Fgravity1 Fgravity2 m1 m2Therefore, Newton’s Second Law Equations are:M1: T1- Fg1 = m1a m2: T2- Fg2 = m2aWhat is a pulley?As shown above, these are machines that change the direction of forces. What does it mean to be in equilibrium?All forces are balanced. Forces are vectors, so this is true for all components of the forces on an object or system.Lecture 10 (October 1)Dynamics (continued)What is friction and why does it happen? What kinds of friction are there and what is the difference between them? What is the Normal force?Friction is a force that opposes motion of two or more objects that come in contact with one another. It happens because of slight electromagnetic bonding that occurs between the surfacesof the objects in contact. There is static and kinetic friction. Static friction is the friction that keeps and object from moving when a force is applied. This is given by the equation fstatic = µstaticN. µstatic is the coefficient of static friction. Kinetic friction is the friction that acts on an object while it is in motion. Kinetic friction is given by fkinetic = µstaticN. N in both of these equations stands for the normal force. Normal force is the force that acts perpendicularly to thesurface that is causing the force on an object. Its magnitude is found by identifying all of theforces that act perpendicular to the surface and adding these together, paying attention to the direction of each force.Lecture 11 (October 3)EnergyWhat is energy and its connection to work? What is work? Can work be negative?Energy is an objects ability to do work. Work is the product of displacement and an applied force. These must be in the same plane for work to be done. The equation W = Fllcosθd gives us the magnitude of work. Fll simply tells us that the force is in the same plane as the displacement.Work can be both positive and negative, work is positive when force and displacement are alongthe same plane and in the same direction. Work is negative when force is along the same plane as displacement, but in the opposite direction.Lecture 12 (October 6)Energy (continued)What if the applied force is not constant? What do we use to find work? What is the force of a spring dependent on?If the applied force is not constant, then we cannot use the previous work formula. For example,a spring exerts a simple but variable force. To find work in a spring we must look at the force equation of a spring, Fspring = -k∆x =-k(x-x0). ‘k’ is the spring constant, which is unique to each spring. The x0 is the equilibrium of the spring, the force of the spring is always working to get back to this neutral position. The force of a spring depends on position and that depends on time. Then we use the equation W= ½k(∆x)2, to find the work done by the spring.What is kinetic energy? How do we find kinetic energy?Kinetic energy is the energy of motion. Kinetic energy is given by K= ½ mv2. Then work can be defined as the change in kinetic energy. Kinetic energy change generally means a change in speed due to a net force that causes an object to accelerate.Lecture 13 (October 8)iEnergy (continued)What is potential energy? What are the special kinds of potential energy? How do we find potential energy?Potential energy is the energy of configuration or position. We can use this to find work as well, as the change in potential energy. This is due to an external force that moves an object with aconstant speed and changes its position. There is spring potential energy and gravitational potential energy. Spring potential energy is given with reference to x0, where the spring has zeropotential energy. Stretching the spring to xf gives the spring potential energy, found with the equation U= ½ kx2. When the