Module C
 Visualizing Forces
 

Page 83: Questions # 1 to 7 inclusive [answers in bold print] 

1.    How is force defined?

Force is anything that  changes or tends to change the state of motion or the shape of a body or object.

2.    Name the four properties of any force.

Magnitude, Direction, Point of Application and Line of Action.

3.    How is weight defined?

Weight is the amount of force applied to a body by the gravitational pull (force) of the earth.

4.    What quantity is the measure of a system's ineria?

Mass is the quantity that is the measure of a body's inertia.

5.    Rank the following objects in order of most massive to least massive: (a) a basketball, (b) a shot, (c) a baseball, (d) a volleyball, (e) a Frisbee, (f) a medicine ball, and (g) a golf ball.

The mass of a body can be determined from its weight on earth; therefore, the masses of the objects can be ranked according to one's estimation of their relative weights or by actually weighing them.  One such estimation of probable order is: medicine ball, shot, basketball, baseball, volleyball, golf ball, Frisbee.

6.    Rank the objects listed in item 5 in order of most weight to least weight.  Compare the two rankings of mass and weight.  Are they the same or do fiferences occur?  Explain.

By actually weighing each of the objects in question 1, it will be learned that the rankings of mass and weight are the same because the greater the mass, the greater the force of gravity on that mass.

7.    If the total human body is the system that youare examining, what is the single point you should folow to describe the body's motion?

For any body or group of bodies whose movement is to be studied, the center of gravity of the body or group of bodies is the point that is used to represent the system.

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Page.89: Questions # 1 and 3 [answers in bold print]

1.    Identify or calculate the four properties of each of the forces shown in Figure C.12.  Determine the magnitude, suing a scale of 1 cm - 20 N of force.  Identify the point of application with a P and the lines of action with dashes.

Refer to Figure C-1 for the four properties of a force.  The instructor may want to enlarge Figure C-12 on handouts if the actual drawings with calculations are to be turned in.

3.    A runner pushes downward with 300N of force and backward with 400N of force against the ground.  Using a protractor and ruler, perform this vector analysis:  Draw to scale the two force vectors, considering magnitude, direction, and point of application.  Find the magnitude and direction of the resultant force applied to the ground by the foot.

A horizontal vector is drawn to represent 400 N of force directed backward parallel to the ground and a downward directed vector is drawn perpendicular to the ground to represent 300 N (both are drawn to a scale, such as 1 cm equals 100N).  After the rectangle is completed, the resultant is drawn from the tails of the original vectors at the point where the foot touches the ground to the diagonally opposite corner, and its magnitude is found by measuring and converting centimeters to Newtons.  R is 500N directed 37 degrees below the horizontal; the angle is found by measuring with a protractor.  The resultant force may be calculated by using the Pythagorean theorem.