The first exam will be on Tuesday, September 25, room 109 in Heldenfels building. Section 807 and half of the Section 808 (students with last name starting with A to H) will have exam from 7 to 8 pm. Students from Section 808 with last name starting with J to Z, and all students from Section 809, will have exam from 8:15 pm to 9:15 pm. Students that have the exam from 7 to 8 pm will not be allowed to leave earlier than 8 pm. No calculators and cell phones in the room during the test. Don’t use your own scratch paper; there will be plenty of it in the room. Please DO NOT FORGET TO BRING YOUR STUDENT ID!
Ch. 6 Quiz A block of mass M is pushed against a vertical surface. The coefficient of friction between the surface and the block is equal to . If angle is known, what is the minimum magnitude of P to hold the block still? P
What is included? Chapters 1-6 Kinematics, 2D motion, vectors, Newton’s Laws
DO NOT use Const acceleration case formulas when acceleration is a function of time. You have to integrate or differentiate! What are the Const acceleration case formulas?
Q DO NOT forgetthat Fp has two components: Fpcos θ and Fpsin θ
Do Not Forget to • Write down what is given and express the answer in terms of what is given • Box the answer
A Recipe for Solving Second Law Problems • Sketch • Isolate the body (only external forces but not forces that one part of the object exert on another part) • 2. Write down 2nd Newton’s law Choose a coordinate system Write 2nd Newton’s law in component form: 3. Solve for acceleration
Pulling Against Friction • A sled of mass m is on a surface with coefficients of kinetic friction mkand static friction s. You pull with a constant force F at an angle Q. The sled does not leave the surface and moves to the right. • What is a minimum force needed to bring the sled in motion? • What is the magnitude of the acceleration? • What angle maximizes the acceleration?
Friction Two types of friction: • Kinetic:The friction force that slows things down • Static:The force that makes it hard to even get things moving
Kinetic Friction For kinetic friction, it turns out that the larger the Normal Force the larger the friction. We can write FFriction = mKineticFNormal Here m is a constant Warning: THIS IS NOT A VECTOR EQUATION!
Static Friction This is more complicated For static friction, the friction force can vary FFrictionmStaticFNormal Example of the sled: If I don’t push, what is the static friction force? What if I push a little?
Box on an inclined plane A box with mass m is placed on a frictionless incline with angle qand is allowed to slide down. • What is the normal force? • What is the acceleration of the box? q
The advantage of a pulley What minimum force F is needed to lift the piano of mass M?