What weighs about 1 N?

an apple

What weighs about 10N?

Large Textbook

or a 1 liter bottle of soda

What weighs 100N?

3 Gallons of milk

What weighs 1000N?

Mr. Nystrom wearing a backpack full of books

If you weigh 600N and are hanging on a rope, you are pulling down 600N on the rope. The rope is pulling ______

up 600N on you!

If you weigh 600N and jump off of a building, do you accelerate towards the earth?

Does the earth accelerate towards you?

YES, you accelerate toward the earth and YES the earth accelerates toward you (it is hard to see)

How can you think of gravity to help you “see” objects being pulled towards eachother?

Imagine a stretched spring between them. A spring between two cars may pull them both together at the same acceleration, but a spring between a car and a skateboard will mostly pull the skateboard more. MASS RESISTS ACCELERATION

Why don’t you see the earth move when you jump up?

It is so massive that it barely moves

If force = mass * acceleration, then acceleration =

FORCE / MASS

if force = mass * acceleration, then mass=

FORCE / ACCELERATION

When you fire a gun, the force on the bullet is equal to the _____________

force on the gun

When you fire a gun, the momentum of the bullet just after the shot is fired equals____

the momentum of the gun just after the shot is fired.

why does a bullet go faster forward than the gun moves backwards if they have the same force?

(and they have the same momentum…)

the gun has more mass. If you push a roller skate with the same force that you push a bus, the rollerskate will accelerate faster!

What is a way to think of mass when it comes to moving things?

MASS RESISTS ACCELERATION

(this is what we call inertia, mass is a measurement of inertia)

If you have a force and need to find the X and Y component, how do you do it?

The force given is always the hypotenuse of a right triangle.

Draw an X and a Y component, making a triangle.

The closest (adjacent) side= FORCE * COS (ANGLE) and for the far (opposite) side= FORCE * SIN (ANGLE).

COSINE for CLOSE SIDE

How do you combine forces mathematically?

break the forces down into X and Y components and then combine all the X components and all the Y components into a resultant X and resultant Y. Sketch it. The diagonal of the rectangle made with those is the resultant force and it goes in that direction.

How do you sketch the resultant force of two vectors?

USE THE PARALELLOGRAM RULE.

When you get the resultant X and the resultant Y, how do you find the magnitude of the resultant force?

use pythagorean theorem. R = sqrt (Fx^2 + Fy^2)

When you get the resultant X and the resultant Y, how do you find the direction (angle) of the resultant force?

angle to horizontal = tan-1 (Fy/Fx)

What is momentum?

MASS * VELOCITY

What are two ways to change momentum?

Change the mass or change the velocity

If two objects have the same velocity, the one with the larger mass has _____ momentum

larger

if two objects have the same mass, the one with less velocity has _____ momentum

less

As velocity increases, momemtum _____

increases

What is impulse?

Change in momentum, or FORCE*TIME (a force over an amount of time changes momentum)

What is “FAT MAV?”

F delta T = m delta v

delta (the triangle) means “CHANGE IN”

(force * change in time = mass * change in velocity)

F = ma can be changed to what?

change the a to (delta v / delta t) so you get:

F = m (delta V / delta T)

this is another version of fat mav.

What does “conservation of momentum” mean?

Momentum before = momentum after

What are the three conservation of momentum equations we use in this class? (along with the situations

mv+mv= mv + mv (separate before and after).

(m+m)v = mv + mv (stuck together before).

mv+mv= (m+m)v (stuck together after)

What changes the momentum of an object?

Applying a force over an amount of time.

THISS IMPULSE

Impulse changes momentum.

mv = Ft what does this say?

Generally used when something crashes.

momentum before = impulse

(because all of the momentum is lost in a crash).

Mass times velocity before = Force (time)

What is an elastic collision?

When all KINETIC energy is preserved

momentum before = momentum after.

(we solve problems like this, but in reality, energy is usually lost through sound and heat)

What is an inelastic collision?

When some momentum, some energy is lost through heat, sound, etc

What types of collisions do we usually consider when solving problems in class?

We assume they are elastic collisions (similar to how we often ignore friction).

***EXTRA CREDIT CARD*****

need to show work.

If a 1 kg ball moving at 20m/s makes a 4cm dent in a wall. What was the force? (4cm = .04m)

using F = m (delta v / delta t).

We have m= 1kg, delta v = 20m/s- 0= 20m/s all we need is time.

To find time, you need to user d = VT , or T = D/V…

in this case, average velocity is (20 + 0)/2 = 10m/s ..

so T = .04m/ 10m/s = .004 sec.

F = 1 (20/.004) = 5000N

Which causes more impulse, a 1kg ball hitting you at 10m/s and stopping, or a ball bouncing off your head and traveling back at 5 m/s?

A ball bouncing causes more of an impulse.

Impulse is change in momentum.

The ball that stops velocity only changes 10m/s (from 10 to 0), the bouncing ball goes from +10m/s to -5m/s, an overall change of 15m/s.

The more the velocity changes, the more the momentum changes, which is a larger impulse!

When a cannon is fired, explain how momentum is preserved.

mv(cannon) + mv(ball) before is ZERO. It has to be zero after, so the momentum of the cannon must be in the opposite direction of the momentum of the ball to cancel it out.

They will have the same magnitude, but opposite directions. Right after the cannon fires:

mv (cannon) = mv (cannonball).

How are FORCE and MOMENTUM different?

Force = mass (acceleration)

Momentum = mass (velocity)

Momentum exists when something moves at a constant speed, or when it is changing

Force is ZERO if something is moving at constant speed. Force only exists when velocity is changing.

Both Momentum and force are zero if it is at rest (in equilibrium).

When solving right triangles using trig, what do we do first?

LABEL THE H, the O and the A, then figure out which ratio to use:

soh, cah or toa

Where is the hypotenuse?

It is the longest side. Always the side across from the right angle. It is the diagonal.

Where is the “opp” side?

If you imagine standing in a triangular room in the same corner as the angle. The opposite side is on the wall across the room from you.

Where is the “adj” side?

if you imagine standing in a triangular room in the same corner as the angle. The adjacent side is the side you can touch that is not the hypotenuse. It makes the angle with the hypotenuse.

What does the word “adjacent” mean?

It means “NEXT TO”

What does SOH CAH TOA stand for?

sin angle= opp/hyp cos angle = adj/hyp tan angle = opp/adj

What are other words for “UNTRIG?”

arctrig, or inverse trig. (arcsin, arctan, arccos or inverse sine, inverse tan or inverse cos)

When do you have to use trig-1, aka UNTRIG,inverse trig, or arctrig?

when you are trying to FIND AN ANGLE (not a side)

What are the three possible situations when solving trig ratios?

- solving for angle: trig x = A/B just untrig: X= trig-1 (A/B) 2. solving for numerator: trig angle = X/B just slide the B: X= B trig angle 3. solving for denominator: trig angle = A/X just switch: X = A/(trig angle)

How do you find the side closest to the angle (adjacent to the angle) if you have the hypotenuse?

hyp * cos angle

How do yu find the side furthest from the angle (opposite the angle) if you have the hypotenuse?

hyp * sin angle

How to solve for x: trig X = A/B

UNTRIG: trig-1 (A/B) = x

How to solve for x: trig angle = X/B

SLIDE: B trig angle = x

How to solve for x: trig angle = A/X

SWITCH: A/trig angle = x

How to solve triangles when there are no angles given?

PYTHAGOREAN THEOREM

If you are given the hypotenuse and need to find the side closest to the angle, how do you find it?

hyp * cos angle

If you are given the hypotenuse and need to find the side opposite the angle, how do you find it?

hyp * sin angle

When you have sides of a triangle, but are trying to find out what an angle is, what do you have to use?

trig -1 (untrig, inverse trig, arctrig)

What are other names for UN-TRIG?

arc trig, inverse trig

What to the interior angles of a triangle add up to?

180 degrees, since a right triangle already has a 90 degree angle, the other two angles are complementary (add to 90)

sin 70 = cos __

20

cos 50 = sin __

40

sin 50 / cos 50 = tan ____

50

sin m = cos ___

90-m

cos g = sin ____

90-g

sin f / cos f = tan ___

f

How are FORCE and MOMENTUM similar?

Both are ZERO for objects at rest.