Implications of Mechanics on Objects

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  • 0:06 Mechanics
  • 1:04 What is Motion?
  • 1:59 Rest
  • 2:43 Acceleration
  • 3:06 Force is Responsible…
  • 4:16 Simple and Complex Movement
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

Forces act on objects causing them to move. Mechanics is the field of science designated to the study of moving objects. This lesson describes how forces act on objects resulting in motion. Examples are used to describe how forces interact resulting in both simple and complex movement.

Implications of Mechanics on Objects

Everything in the universe is moving at any given moment.
Everything Is Moving

Did you know that everything in the universe is moving? Even objects that appear to be completely still are actually moving. Let's do a quick experiment. If you can manage to do so, sit completely still for five seconds. Here, I'll count while we do it. One, two, three, four, five. During those five seconds you know what, you were actually moving with a speed of about 1,000 MPH. That's how fast the earth is spinning on its axis; therefore, that's how fast you are actually moving while sitting still on your chair. For that matter, the earth is orbiting the sun, and the sun is moving around our galaxy. Wow, that's a lot of motion! So, mechanics - that is the field of science designated for the study of moving objects. Scientists have been studying moving objects for centuries.

What Is Motion?

Motion is defined as the movement of an object. Inertia is the tendency of an object to resist changes in its state of motion. As discussed, all objects are moving, even those that appear to be completely still. Furthermore, all objects have inertia and thus they tend to resist changes in their motion. The state of motion of an object is defined by its velocity. Velocity is the speed at which an object is moving with regard to direction. Thus, inertia can be phrased as the tendency of an object to resist a change in its velocity. For example, a car may be traveling with a velocity of 65 MPH to the west. In other words, the car's state of motion is 65 MPH to the west. As the car has inertia, it will tend to maintain its velocity of 65 MPH to the west.

A car traveling at 65 MPH to the west will tend to maintain this velocity due to inertia.
Car Velocity

At Rest?

An object at rest is said to have zero velocity. Therefore, its state of motion is also zero velocity. I just told you that all objects are moving. So, what does it mean to say an object is at rest has zero velocity? An object is said to be at rest if it is not moving relative to some reference point. Let's look at an example; my computer is at rest on my table. It is not moving relative to the table. The table is not moving relative to the floor that it is sitting on within my house, and my house is not moving relative to the earth. The earth, as we know however, is moving.


If an object changes its velocity it has what we call acceleration. If an object increases its velocity, we call that positive acceleration. If an object decreases its velocity, it has negative acceleration. Any time an object accelerates, it changes its state of motion.

Force Is Responsible for Motion

Now that we've established that everything has motion, let's consider what is responsible for causing that motion? The answer to this question is force. A force is any influence that causes an object to change its shape or motion. There are usually multiple forces acting on an object at any particular time. For example, a ball at rest on the ground is pulled down by the force of gravity and it's pushed up by the force of the earth's surface. Additionally, the air molecules are constantly bombarding the ball on the outside as well as the inside. All these forces have magnitude; that is they have size. If the forces are acting in the same direction, then they are added together and cause motion to occur in the same direction. If the forces are acting in opposite directions, those forces are subtracted from each other and they cause motion in the opposite direction. The units of force are usually expressed as Newtons in honor of Sir Isaac Newton who did much to advance our understanding of mechanics.

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