Aim (Part One): What is a drag force? What is terminal velocity?
Do Now:
A 4.5 N force pushes a block on a friction-less surface, producing an acceleration of 2.5 m/s2. Suppose a second block (4.0 kg) is then dropped on the first. What is the magnitude of the acceleration of the two-block system if the same force continues to act? 71. A 0.60 kg fishbowl is lifted from the ground. What is the smallest force needed to lift it? Describe its resulting motion.
Fnet = Fscale + Fg = 0Fscale = - FgFscale = - (-mg) = mgFscale = (0.60 kg)(9.8 m/s2) = 5.88 N
If Fnet = 0, then a = 0If a = 0, then motion is constant velocity
Aim (Part One): What is a drag force? What is terminal velocity?Drag Force Force exerted by fluid (air or water) on object moving through fluidEx: air resistance Opposes motion Increases with objects velocity Object in free fallNo viAccelerating downward, a = gt = 0 sv = 0 m/st = 1 sv = 9.8 m/st = 2 sv = 19.6 m/st = 3 sv = 29.4 m/s Reach a point where Fnet = 0 Fdrag = -Fg
Object stops accelerating Continues to move with constant velocity
Terminal velocityDown the Rabbit Hole: Drag Force and Terminal Velocity
Hannah is going skydiving for her birthday. She has a mass of 68 kg, and jumps from rest. She reaches terminal velocity after falling for 15 seconds. (a) What drag force is exerted on her when she reaches terminal velocity?(b) What is her terminal velocity? Aim (Part Two):How is Newtons 3rd Law used?Interaction Pairs Newtons 3rd Law:FA on B = FB on A
Two forces, in opposite directions, with equal magnitude
Two free body diagrams
F boy on snowballF snowball on boy
Two blocks, masses 4.3 kg and 5.4 kg are pushed across a frictionless surface by a horizontal force of 22.5 N. What is the acceleration of the blocks?What is the force of the 4.3 kg block on the 5.4 kg block? What is the force of the 5.4 kg block on the 4.3 kg block?Tension force exerted by a string or rope
FT
equal to weight of all forces hanging from rope
A 45 kg child sits on a 3.2 kg tire swing. What is the tension in the rope that hangs from a tree branch?Fnet = Fscale + FgFnet = Fupward + FgscaletensionSnow White has been sent by the Queen to fetch a bucket of water from a well, so that she can clean the castle. If the rope attached to the bucket is guaranteed not to break as long as the tension does not exceed 450 N and she fills the bucket until it has a mass of 42 kg, what is the greatest acceleration that she can give the bucket as she pulls it up from the bottom of the well?Two blocks, one of mass 5.0 kg, and the other of mass 3.0 kg, are tied together with a massless rope. This rope is strung over a massless, resistance-free pulley. The blocks are released from rest.
Find (a) the tension in the rope, and (b) the acceleration of the blocks.
[Hint: you will need to solve a system of two equations.]5 kg3 kgNormal Force contact force exerted by a surface on another object perpendicular to surface, upward
F normalF gravity
F normal puts system in equilibriumAndy and his family are packing up their car, getting ready for him to move to college. They put one 7 kg crate of books in the car, and then put a 2 kg box of action figures on top of it. What is the normal force on the 2 kg box?What is the normal force on the 7 kg box?
