(1) What is the difference between a law and a theory? (Between an axiom and a hypothesis?) A theory starts off as an idea and then, over time, as it is tested and tried, it MIGHT become so firmly accepted as a universal, fundamental concept, that it gets to be called a law. A hypothesis is a proposal made to test a theory: "If asteroid Anglabob 876 is at 3.4 AU and currently in the constellation Scorpio, then, if Kepler's theory of elliptical orbits is correct, it should make its retrograde loop between Saggitarius and Aquarius between March and July next year". An axiom is a "self-evident truth" - something which is reasonable to assume before you start making your theory - e.g. "Ah, but you are assuming that asteroid Anglabob 876 acts the same as a planet" - "Yes, naturally, that is axiomatic (you idiot)". A good word to drop at parties.

(2) How many different controls are there in a car for causing it to accelerate? Name each and give a brief explanation of each. (Hint: there are 3, at least) Accelerater to speed up, brake to slow down, steering wheel to change direction. Some might also use the gear stick to control speed.

(3) Look back at Galileo's Law of Inertia What was this inertia stuff? Which has more inertia, a brick or a feather? A brick has more inertia than a feather - the greater the mass the greater the inertia. A ton of bricks or a ton of feathers? Aha! Trick question - they both have the same mass - so same inertia.

(4) To ride quickly around an obstacle course you want to ride a vehicle that is which of the following?Ê (a) heavy and able to squash the obstaclesÊ (b) light and maneuverable - LOW inertiaÊ (c) brightly colored to attract attention

(5) In the following diagrams there are plenty of FORCES--yet nothing is moving--why not? In all cases the forces are balanced - there is no NET force. So nothing moves.

6) The original Honda Civic car was a metal shell (plus seats, stereo, etc.;) around the same engine as the Honda 1000cc motor bike. The car and bike engines could deliver the same FORCE, but the car had all that extra MASS. Use Newton's Second Law to show which will have the greater ACCELERATION--the car or the bike? Newton's 2nd law says that the ACCELERATION = FORCE / MASS - so, the greater the MASS, the SMALLER the ACCELERATION. That means that the lower mass bike will beat the car away from the lights.

(7) Pitchers can throw baseballs so that they reach 90 MPH when they reach the batsman. That means the pitcher applies a force that accelerates the ball from 0 to 90 MPH in fractions of a second. Impressive. If baseballs were made of iron or stone instead of rubber and leather (or whatever they are made of) so that the balls were twice their normal mass, how much greater force would the pitcher have to apply to achieve the same acceleration? Newton's 2nd law says that FORCE = MASS x ACCELERATION. This time we are keeping the accerleration fixed but increasing the mass. This means that if we double the mass then you need to double the force to get the same acceleration.

(8) In each of frames A, B and C, how many forces are acting? A - one ball is in uniform motion and the other is stationary - Newton's first law says that there are no forces acting in this case. B - TWO forces here - equal and opposite (N's 3rd law). C - the situation is the same as A (no forces) but with the balls switched.

(9) As a result of the collision between the truck and the bicycle, (a) the change in the bike's velocity is big / little / none (b) The change in the truck's velocity is: big / little / none - this is just using Newton's second law - same force but different masses leads to (inversely) proportionally different accelerations.

(10) Are Laws of Physics the same as Federal Laws -- does the exact wording matter? No, not really - as long is what's going on is clear enough (no one is going to argue over the meaning of "is")

(11) Why can't airplanes fly in space? Why do we need rockets? Planes get lifted of the ground by the pressure difference between the top and bottom of the wings - this means there needs to be sufficient of air pressure. In space there is too little air pressure. Rockets, which send the spaceship forward by throwing gas out the back, can work in vacuum.

(12) Imagine you are swinging a ball on a string in a circle above your head, with the ball taking 2 seconds to complete a circle. (a) Is the object on the string at rest, in uniform motion or accelerating? It is changing direction - so it is accelerating.

(b) Are you pulling or pushing the string?Pulling - applying a force into the center.

(c) Use Newton's laws of motion to describe what is happening. You are applying an inward force. As a result, the object on the string is accelerating (Acceleration = Force / Mass) by changing direction.

(d) Then you let go of the string. What happens? The object keeps going in the direction it was at the instant you let go - off at a tangent to the circle.

(e) How is what happens in (d) consistent with Newton's 1st law of motion? The force is removed. So the object continues in uniform motion - a straight line, constant speed.

(13) Earth orbits the Sun at a constant speed of 30 km/sec. (a) How is this consistent with Newton's theory that the Earth is continuously accelerating towards the Sun?ÊSame as the object on a string - there is an inward force (gravity of the Sun) pulling on the Earth. As it orbits, the Earth changes direction - it is accelerating.

(b) Suppose the Sun suddenly disappeared--poof! What would be the Earth's motion? Just like the object on the string when you let go, the Earth would continue in a straight line, tangent to the original orbit.

(14) If the Earth and Moon are feeling the same amount of force, why does the Moon orbit the Earth rather than the Earth orbit the Moon? The FORCES are the same, but the ACCELERATIONS are not the same. The Moon is much less massive then the Earth (81 times less) so that the acceleration felt by the Moon will be 81 times greater than the acceleration felt by the Earth. So the Moon orbits the Earth and while the Earth DOES move around their common center of mass, the movement is tiny and the center of mass is very close to the center of the Earth.