Test Review Hand in day Work/power Friday PS 10-19 Test Review Hand in day Work/power

Review for test on Monday Forces Definition- any push or pull on an object Units are NEWTONS Applied forces: contact forces

Frictional forces The force that resist the movement of one surface over the another Determined by surface conditions, and the forces pressing the 2 surfaces together Static friction is greater than sliding friction

Equation Ff = μ Fn

Coefficient of friction No units Measures the interaction between the two surfaces .1 nearly smooth .99 very rough

Normal Force The force that ground reacts with Perpendicular to surface and away from surface At this point generally = to weight of object pressing down on surface

Forces Balanced forces = when all the forces acting on an object cancel each other out Unbalanced forces = when all the forces do not cancel each other out (more force on object in one direction than in others)

Net force The combination of all forces on an object For balanced forces Fnet = 0 At rest or at constant velocity For unbalanced forces Fnet ≠ 0 acceleration

To calculate net force Combination of all forces on object Concentrate on forces in dimension of motion If forces are in same direction, add them If forces are in the opposite direction, subtract them

Weight, mass Weight = the force due to gravitational pull on an object W = mg g = 10 m/s2 on earth Mass = the amount of matter that makes up an object Differences? Similarities?

Inertia Is the measure of an objects resistance to change in its motion Directly related to the amount of mass

Newton’s 3 laws !st 2nd 3rd When does an object change its motion (accelerate)?

Free body diagrams FBD’s purpose: To visually show how the forces are arranged on an object Components of a free-body diagram Forces Object Direction arrow

FBD Where do all but the direction arrow originate in the diagram? How are the forces of air resistance or friction drawn on FBD? How is the force of gravity drawn on any FBD?

2nd Law problem set up #1 Draw free body diagram #2 Calculate as many of the forces on the FBD as possible #3 What are the givens? #4 what do you want? #5 what equations will connect the givens to what you want #6 solve and check

2nd law problems Using Fnet = ma Units for each part are…? Triangle set-up

2nd law problem A 200 kg crate is pushed horizontally with a force of 700 N. If the coefficient of friction is 0.2: Calculate the acceleration Calculate the net force If its initial velocity was 3 m/s, how fast is it moving after 15 minutes How far did it travel in 15 minutes

Example Nicole slows down in her BMW from 15 m/s to 3 m/s in 42 seconds. What is the mass of her car if the net force on it is 7312 N?

Free Fall Any object that moves under the influence of only the force due to gravity Thrown, Dropped objects Acceleration = 10 m/s2 or (9.8)

What is the velocity and acceleration value at the following points in time of a heavy object being thrown upwards at 5.0 m/s? Just when it leaves the hand? At the apex of its flight? Just before it is grabbed by the hand?

Terminal velocity The maximum velocity reached by a dropped object Occurs when the downward gravitational force is matched by the upward force of air resistance Air resistance depends on surface area and speed of object

Action and reaction forces Identification in the real world Equal and opposite Applied to different objects May have different effects

Metric conversion 0.302 km  _________ mm