TODAY AND TOMORROW 1) New video up you need to watch/note 2) Some brief reminders of ramps, then new with ramps/pulleys 3) We spend time at the boards confirming a quarter of knowledge.

THE H OMEWORK Questions? Concerns?

RAMP REVIEW Instead of X and Y, we are going to rotate to a ‘New X’ and ‘New Y’: ‘New X’ : Down/Uphill ‘New Y’ : Perpendicular to the hill Weight in X is the SIN of the weight. Weight in Y (perpendicular to ramp) is the COS of the weight

VOTING Here is a block that is currently moving on a ramp. Which of these are true (2 correct answers) A) The friction will act uphill on the block B) The acceleration of this block will be less than gravity C) The normal force is equal to the weight of the block D) The amount of mass has no effect on the acceleration of the block in this case.

R AMPS …T HE FBD Block is in contact with 1 thing. With friction, that makes 2 forces. Plus 1 non-contact force. But…it will accelerate down the ramp. Lets draw the forces

T HE IDEA The friction and normal force are not in X or Y. But the block will also not accelerate in X or Y. So we will create a NEW frame of reference to make the physics easier. Downhill/Uphill is X, Perpendicular to ramp is Y So the weight is now not in the new X or Y, need to find its X and Y components

Weight 1) Lets draw in the parallel and perpendicular parts of the weight Weight perpendicular to ramp (Y) Weight parallel to ramp (X) Ramp angle 2) The two angles are the same due to geometry 3) Using Sin and Cos we can find the X and Y parts of the weight MgSin (θ) MgCos (θ) θ

4) Draw the forces now on the block in X and Y Weight perpendicular to ramp (Y) Weight parallel to ramp (X) MgSin (θ) MgCos (θ) Normal Force 5) Depending on the way the block is moving, draw friction Friction if moving downhill Friction if moving uphill

L ETS CREATE N ET F ORCE E QUATIONS AND SOLVE FOR THE ACCELERATION ! Moving downhill:

L ETS CREATE N ET F ORCE E QUATIONS AND SOLVE FOR THE ACCELERATION ! Moving Downhill

L ETS CREATE N ET F ORCE E QUATIONS AND SOLVE FOR THE ACCELERATION ! Moving uphill:

L ETS CREATE N ET F ORCE E QUATIONS AND SOLVE FOR THE ACCELERATION ! Moving uphill:

OLD VOTING… A MOVING BLOCK A) The friction will act uphill on the block False…depends on which way the block moves B) The acceleration of this block will be less than gravity True…The X part of the weight is causing the acceleration, which is less than the total weight C) The normal force is equal to the weight of the block False…the normal force is equal to the D) The amount of mass has no effect on the acceleration of the block. True…The mass term is in all three cancel out if you just deal with one contact (surface). If there was another force then it WOULD matter

A ND N OW A LL T OGETHER Here is our next thing to tackle…tomorrow.

NOW Lets review the major ideas through examples. Why on the boards….