1st Semester Exam Review

Math and Metrics

Sig Fig Rules:505 – zero is significant500 – zeroes not significant0.05 – zeroes not significant5.00 – zeroes significant0.0500 – only zeroes at the end are significant

Most commonly missed rule: zeroes that are after the decimal and are final zeroes are significant

Math and Metrics

Be able to convert (m/skm/h) (mcm), etc

Be able to convert from standard form to scientific notation and vice versa

Example: change 0.0002490 to scientific notation

Example: change 4.12 x 106 to standard form

Linear Motion

What is the distance?

What is the displacement?

Speed vs Velocity

• Speed = scalar• Velocity = vector

S = total distance / total time

V = displacement / total time

Acceleration

• The rate of change of velocity• All acceleration we have studied has been

constant• + v and + a = speeding up• + v and – a = slowing down• - v and + a = slowing down• - v and – a = speeding up

a = vf - vi

t

d = vit + ½ at2

vf2 = vi

2 +2ad

Free Fall

• An object is considered in free fall when it is moving only under the influence of gravity.

• An object that is thrown up in the air is in free fall (even when it is moving up).

• When an object is in free fall, its acceleration is -9.8 m/s2.

• The entire time the object is in free fall its acceleration is -9.8 m/s2 even when the object is moving up.

Graphing• Know how to draw graphs of:d vs t; v vs t; a vs tFor object:At restConstant speedSpeeding upSlowing downDroppedThrown up and comes back down

Graphing

• Be able to identify what v vs t graph belongs to what d vs t graph

Vector Addition

Vectors

Know how to add vectors in the same direction, in opposite directions and at right angles.

Be able to find components of a vector (i.e. sides of a triangle)

Vectors

S = d/t can be used with vectors

You must match up speed and distance

Projectiles

• Projectiles move at constant velocity in x direction

• Projectiles have acceleration -9.8 m/s2 in y direction

• Time for a falling object is the same as time for an object to hit the ground if fired horizontally.

Forces

• Newton’s 1st Law: Object in motion stays in motion, object at rest stays at rest UNLESS acted on by an outside force (also called law of inertia)

• Newton’s 2nd Law: Fnet = ma

• Newton’s 3rd Law: For every force there is an equal and opposite force

Forces

• Force is not needed to maintain motion.• Object with zero net force is in equilibrium• Object in equilibrium will have no change in its

motion (either at rest or in motion at a constant speed)

• Inertia is not a force. It is the tendency of an object to resist a change in its motion.

Forces

• Inertia is directly proportional to mass (more mass, more inertia)

Forces

• Problem solving:Basic: net force given? Fnet = ma

Advanced: multiple forces acting (i.e. tension and weight, or Fapp and Friction) draw FBD and write equations (U-D = may) (R-L = max)

Force

• More Problem Solving

Equilibrant force: use pythagorean theorem to find resultant force equilibrant force is same value 180 degrees in other direction

Momentum

• P = mv• J = Ft• Momentum is changed when an impulse acts

on an object.• The impulse is equal to the change in

momentum.• Ft = mΔv

Momentum

• Vector quantity• Always conserved in a closed system (no

outside forces presenti.e. friction)

Momentum

• Consequence of Impulse-Momentum Theorem: if time of collision is extended, force will decrease.

• Extending time has NOTHING to do with the change in momentum, also can’t change the value of impulse.

Momentum

• Inelastic: objects collide and stick together• Elastic: objects collide and bounce apart

• Momentum is conserved in both types of collisions

Concept Questions

• When you do throw that bowling ball while standing on the pond:

How does your final velocity compare to that of the ball?

How does your final momentum compare to that of the ball?

Assume no frictionAns: The ball has a greater velocity, you have

equal momentum