8th Grade: Homework tonight will be to work on the Moon Observation Project, due at the end of the month, and Answer questions and define vocabulary to Complete your Blueprint (Study Guide) for your Mid Term Exam. Be prepared to take it tomorrow (without staying up late).

Q) Why can’t a roller coaster go up a hill that is higher than the hill it just came down?

A) The roller coaster that's gone down a small hill won't have enough energy to get up a bigger hill, plus it loses efficiency- some of the roller coaster's kinetic energy is lost to friction, noise and other transformations of energy.

Q) What happens to the thermal energy in water when hot and cool water are mixed?
A) Thermal energy moves from hot water to the cool water, temperature of both kinds moves towards the middle.

Key vocab:
Acceleration in m/s2 – Acceleration is the rate of change of velocity over time. Objects fall to Earth at 9.8m/s2 (9.8 m for each second the object falls)


Speed – The rate at which an object moves, equal to the distance traveled per time interval. s = d/t

Force in Newtons (N):  1N = 1 kg-m/s2. The force (a push or pull) it takes to push a 1- kg mass over a distance of 1 meter in 1 second, for each second the force is applied.

Inertia – the resistance an object has to a change in its motion. Ex: unbelted passenger in a car that stops suddenly
  Friction – force that resists the movement of another object or substance.

Balanced forces – are when forces push or pull in different directions, with equal strength.

Unbalanced forces - Forces that push or pull in different directions with unequal strength. Acceleration happens only with unbalanced forces.

Net Force - If forces are unbalanced, there is a net force. The object is accelerating. In the diagram above, the box will accelerate to the left.

Center of mass - the point where distribution of an object's mass is centered. This is a location, not a amount of mass.
Analysis Questions:
a) What is a car’s speed in m/s if it travels 5 meters in 0.1 seconds?

     S= d/t = 5m/0.1 s = 50 m/s

b) What would happen if you threw a baseball in outer space? Explain using the words inertia and friction.
     A baseball thrown in outer space, like all objects, would have inertia. According to Newton's 1st Law of Motion, an object in motion will stay in motion at the same velocity (speed and direction) until acted on by an unbalanced, outside force.  Objects thrown on Earth often slow down due to gravity and friction, but friction would not slow down the baseball thrown in space. Friction is a force that opposes the motion of another object and is caused where surfaces in contact are moving relative to each other.  Matter is very spread out in space, so the baseball is unlikely to come into contact with other matter which could cause resist the baseball's motion and cause it to slow, change direction, or stop from friction. Nothing in the facts provide information about how close the baseball is thrown to Earth or another object whose gravity is sufficient to change the path.  Based on the facts given, the baseball would continue to travel at the  same speed and direction.
c) Which has more inertia, a basketball or a bowling ball? Why?
The bowling ball has more mass, therefore more inertia.
d) What are Newton’s Three Laws of Motion?
1. The Law of Inertia
2. F = m x a
3. Action /Reaction
e) Draw an example of unbalanced forces. What is the net force?
                <--5n--- nbsp="nbsp">net force = 5N
Vocab:
Force (N) - A force is a push or a pull and a Newton (N) is a unit of force.

Mechanical Advantage (Output Force/Input Force)-- Mechanical advantage is the number of times a machine multiplies the effort force. ex: if you put 10 N into moving a box using a lever, and the output (force to move the box) is 20 N, then 20N/10N gives you a mechanical advantage of 2.

Efficiency (Output work/Input work x 100%) - Efficiency is the ratio of
work output (meaning the work done by a machine) to
work input(meaning the work you put into a machine)
multiplied by 100%. 
Efficiency is always less than 100%, because some effort is always lost to waste, such as friction, noise or heat. 
Ex: if you put 500 N into pushing a car that ran out of gas, and the output (force to move the box) is 250 N, then Efficiency = Output work/Input work x 100 =250N/500N x 100 = efficiency of 50%.

Work in Joules (J) - Work = Force x distance, and Joules are a unit of work. One Joule = 1 Newton-meter

a) List the 6 Simple Machines and give an example of each. Lever, inclined plane, screw, wheel and axle, pulley, wedge.
.......1. Lever (ex: seesaw, bottle opener, wheelbarrow, elbow); ... 2. inclined plane (ex: skateboard ramp, escalator, handicapped ramps like the one at the front of our school, ramp to drive a car into a parking lot;)......3. screw (ex: bolt, spiral staircase, drill bits, ).....4. Wheel and axle (ex: wheels on a skateboard, bike, car, wagon or train; doorknob).....5. pulley (ex: flagpoles, window blinds, garage doors, winches on cars and sailboats and wells).....6. Wedge (ex: knife, doorstop, shovel, axe, nail, zipper).

b) You are moving a house plant from your living room in to the kitchen. How much work does it take to move the plant 12 meters with 5 N of force? Work = Force x distance or W = F x D =                                 5N x 12m= 60N-m or 60J

c) Is putting books into your backpack work, or is carrying your backpack to class work? Why?
Yes. Putting books in your backpack , and carrying your backpack both require you to move something using force across a distance, so it's work.

d) What is the mechanical advantage of a can opener that requires you to exert an input force of 20 N and the opener exerts an output force of 60 N on the can?  Apply the formula: Mechanical Advantage (MA)= Output Force/Input Force = 60N /20N = 3= MA


e) You do 20 J of work while using a hammer. The hammer does 18 J of work on a nail. What is the efficiency of the hammer?
Efficiency
= Output work/Input work x 100%
=  18 J/20 J x 100% = 90%
REmaining answers on Blueprint (Study Guide) are being prepared now. Check back in 10 minutes.

6th grade Homework: Answer questions and define vocabulary to Complete the SECOND half of the study guide for your Mid Term Exam, now scheduled for THURSDAY January 17.

Flash cards will be prepared soon.  Check back in 30 minutes.