Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

force that the stuntman exerts on the air mat and subsequently through the air to the ground.

But you recall from Newton’s third law that for every action there is a reaction equal in magni-

tude and opposite in direction. Therefore, the average force exerted by the ground on the stunt-

man is equal in magnitude toFaverage. Also note that the reaction force will be distributed over

the back surface of the stuntman’s body and thus create a relatively small pressure distribution

on his back. You can see from these calculations that the longer the time of contact, the lower

the reaction force, and consequently the lower the pressure on the stuntman’s back.

Summary

Now that you have reached this point in the text

• You should have a good understanding of what is meant by force and its common units. You
  should also know that there are different types of force. You should understand the tendency
  of an unbalanced force, which is to translate and /or rotate objects. The application of forces
  can also shorten, elongate, bend, and twist objects.


• You should be familiar with the Newton’s laws used in mechanics. These laws are the basis of
  analysis in many engineering problems.


• You should understand what is meant by pressure. For static fluids, you should understand
  Pascal’s law, which states that fluid pressure at a point is the same in all directions. You should
  also remember the relationship between the fluid pressure and the depth of the fluid.
  You should understand what the fluid properties such as viscosity and bulk modulus of com-
  pressibility mean. You should also have a good idea of how hydraulic systems work.


• You should realize that engineers, when designing products, need to know how a selected
  material behaves under applied forces. You should know what material properties mean, such
  as modulus of elasticity, shear modulus, and tensile and compressive strength.


• You should understand that when a force is applied to an object, it can affect the object’s
  state in a number of ways. In engineering, these effects are measured in terms of stress,
  moment, work, and linear impulse. Remember that the intensity of a force acting within the
  material, in terms of pulling it apart, compressing, or shearing it, is measured in terms of
  stress; the effect of a force acting at a distance is measured in terms of creating a moment about
  a point or an axis; the effect of a force acting over a distance is represented by mechanical
  work; and the effect of a force acting over a period of time is measured in terms of a linear
  impulse.

292 Chapter 10 Force and Force-Related Parameters

10.1. Design a mass – spring system that can be taken to

Mars to measure the acceleration due to gravity at the

surface of Mars. Explain the basis of your design and

how it should be calibrated and used.

10.2. In the past, scientists and engineers have used pendu-

lums to measure the value ofgat a location. Design a

pendulum that can be used to measure the value ofgat

your location. The formula to use to measure the

acceleration due to gravity is

T 2 p

B

L

g

Problems

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