Mathematical Important Homework and Test results

While most of you did improve on your first force test score, the test results were very disappointing except in 4 instances. Many of you still fail to grasp the basic concepts of force. You must realize that we are studying the real world, not some arbitrary nonesense. Physics explains what you see and feel every day. It will match your experiences if you observe them and interpret them intelligently.

For example, you all know that the force gravity exerts on an object depends on the mass of the object. The force of gravity on a car is not the same as that on a mouse. IT IS NOT 10! it IS Mass x 10N/kg.

Objects on the ground or on table tops or other surfaces do not fall through the ground, table top, or other surface. In addition to force of gravity, these objects experience a normal force upward and opposing gravity. In the absence of any other vertical forces this normal force is equal to and opposite gravity. These two forces together than add to zero force net perpendicular to the surface.

Gravity does not make things accelerate horizontally.

You know things sliding on ramps do not acclerate at the same rate falling objects do, and that the steeper the ramp the faster they accelerate. This is partly because of friction, but mostly because the force pulling down the ramp is only a component of gravity not the whole Mx10. You know it is easier to walk up a ramp then to climb a vertical ladder. This is why.

Some of you are still in the mode of taking whatever numbers are in front of you and putting them into the simplest equation at hand. For example, several students tried to find the force of tension in the rope between two masses on a horizontal surface by subtracting one mass from the other. Force cannot ever = Mass1 - Mass2 period. Force is not the same kind of quantity as mass. The correct answer is found by applying the fact that the rope is causing the second mass to accelerate. This relationship, F on the object =Mass of object x acceleration of object, is a keystone of classical physics, and something we have been studying through experiments, reports, demonstrations, class problems, and discussions for three weeks.

It seems that your observing demonstrations and experiments and reporting your results; my writing on the board; and our discussing things in class, is not sufficent for you to retain some basic facts Therefore you will turn in as homework the following.

Write clearly ten times each

1)Acceleration in a direction = the sum of the force components in that direction divided by the mass being accelerated

2) The component of a force in a direction is equal to the force x the cos of the angle between the force and the component

3) Force of gravity on an object (N) = Mass of object(kg) x 10 N/kg

4) The unknown force on an object in a direction = Mass of object x acceleration of the object in that direction - all the known force components in that direction, with the signs of the force components indicating whether they are positive or negative in that direction ( - means opposite of positive direction)

5) if the component is in the same direction as the force, then the component = the force


This is due Monday, and failure to turn it in will reduce your quarter grade by 5 points, spread the word.

There will be a retest on Tuesday. Note taking is now required and will be reviewed and graded for the forseeable future. Bring the equipment you need to take notes every day.