Inertia depends on mass. Mass is a measure of the inertia of an object.
Galileo challenged Aristotelian notions about motion by performing experiments.
Newton's first law of motion (Galileo's Principle of Inertia) describes what Galileo had discovered about inertia in his "thought experiments," using inductive reasoning.
A net force is the resultant of all forces acting on an object. Equilibrium exists if the net force is zero. (There must also be no resultant torque.)
An unbalanced force exists when the resultant of all of the forces acting on an object does not equal zero.
If no external unbalanced force acts on an object, its velocity will remain constant (i.e., it will remain at rest if it was initially at rest, or continue moving in a straight line at a constant speed, if it was initially doing so).
If all of the forces acting on an object cancel one another, the resultant vector is zero and no unbalanced force exists. The object is in equilibrium.
An object at rest on a table has its weight opposed by a normal force acting on the object by the table. (Other examples of objects in static equilibrium can be used to illustrate this concept.)
If an object is moving at a constant velocity (including the possibility of being at rest) one can conclude that all of the forces acting on the object must be balanced. The net force is zero.
Many practical applications of Newton's first law are evident in common occurrences.
Inertia can be used to illustrate how objects tend to resist their state of rest or motion.
When analyzing situations involving more than one force acting on an object, it is extremely useful to represent the situation using free body diagrams. Vector addition can be used to determine the net force.
When a net force acts on an object, it accelerates in the
direction of the net force. (Newton's second law)
The acceleration is directly proportional to the force for a constant mass:
The acceleration is inversely proportional to the mass if the force is constant:
If an object is accelerating there must be a net force acting on the object in the direction of the acceleration.
The relationship between the SI units for force and the corresponding fundamental units can be illustrated from Newton's second law.
(i.e., 1 N = 1 kg m/s2)
Newton's third law states that for every action force a reaction force exists which is equal in magnitude but opposite in direction to the action force. This can be illustrated using many common examples.
Forces exist in pairs. If object A exerts a force on object B, then object B will exert a force on object A, equal in magnitude, but opposite in direction.
There are a variety of ways of solving problems in physics. No one method is inherently superior to others, although some methods may have certain advantages in specific situations.
To solve problems relating to force and motion, geometric methods using vector diagrams, trigonometry, or vector component methods are some different ways to arrive at similar results.
Practice in problem solving leads to improved proficiency and a greater understanding of how forces interact with objects.
Free body diagrams are useful in analyzing objects in static equilibrium.
Architects, engineers, and people involved in a wide variety of other related disciplines require a thorough understanding of Newton's Laws of motion in order to design equipment which will not fail when used for the intended application.
Students will increase their abilities to:
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.
. Place the objects on an unloaded
inertial balance. Determine the period of the inertial balance
for each of the objects being tested. Plot the period of the
inertial mass as a function of the gravitational mass. Predict
the gravitational mass of a new object after determining its
inertial mass by interpolating or extrapolating on the graph.
Develop a generalized conclusion about the relationship between
inertial and gravitational mass.
is to
build mobiles. For each arm of the mobile, the sum of the moments
must be zero in order for it to remain in static equilibrium.
This concept needs to be applied in order to build a fully
balanced mobile. Each mobile could have a theme associated with
it. For example, one could be a mobile illustrating Nobel Prize
winners and their accomplishments. Another could illustrate
common units or prefixes in the SI system, and so on. Once the
mobiles have been constructed they can be hung on display in the
room.
A similar, related activity would be to analyze other types of sports equipment in the same way.
Much attention has been placed on using science to analyze and improve athletic performance. Some examples include blood analysis of lactic acid build up near the anaerobic threshold, max VO2 determination, and the detection of banned masking and doping agents which enhance performance. Research some of these or other new developments in sport science.
Observe safety precautions when using skateboards. Wear helmets and other protective equipment.
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Rotational motion should be discussed briefly in conjunction with this and several other activities suggested here.
Repeat several trials, supporting the beam in different positions and using different weights. Repeat using several masses at different locations. Make predictions for other trials, testing the accuracy of the predictions.
Students should be familiar with the idea that the lower an object's centre of gravity, the more stable it tends to be. However, in this paradox, the meter stick is easier to balance if the weighted end is closer to the top. This demonstration might lead to an interesting discussion about balance and stability.
The materials required are:
Assemble the poles according to the diagram shown on the next page. Fasten with string. Cut out a cloth cover. Sew it together. Decorate the cover and attach it to the frame. Often tipi designs came from visions and dreams.
Decide where the entrance will be. Cut an opening for the entrance. Decide how to orient the tipi, depending on the direction of the prevailing wind. Have students identify why the tipi is a stable structure in a strong wind.
Examine the convection currents inside the tipi. This helps to explain why a fire can be lit inside the tipi.
If students are interested in pursuing this further, they could construct a full-size replica of a tipi.