Resolution of forces parallel and perpendicular to inclined plane

In kinematics, we were interested in describing motion. In dynamics, the question is not HOW motion occurs but WHY an object experiences the kinematics that it does in terms of its force interactions with other objects.

Earlier in Kinematics, we described motion in terms of displacement, velocity, and acceleration. Now in Newton's Laws, we describe the changes that occur to the motion of material bodies in terms of force and mass. Force is the cause of acceleration. Make sure you can reproduce the outline at left from memory. Organizing your knowledge base will help retention, conceptual understanding, and self-assessment.

In teaching my course over the years, I have often been asked by students the relative importance of different topics for the MCAT. Although an opinion in terms of the explicit distribution of questions can be fairly straightforward, my answers would tend to go into somewhat greater depth because there is often more to the answer than simply 'what will be on the test'. With regard to the topics of fundamental mechanics, while the basic concepts and classic model problems do directly appear with good frequency on the MCAT, the concepts appear, even more so, indirectly as underpinnings of almost everything else in science. With regard to Newton's Laws, for the MCAT itself, there is the fundamental core you need to come to know intuitively. You need to habitually associate net force with acceleration, for example, or be able to unpack the inclined plane or distinguish kinetic and static friction. But don't leave it at that. Take time and step back. In learning mechanics you are building a foundation for understanding all science.

WikiPremed Resources

Newton's Laws Cards
Chapter from the Wisebridge Learning System for Physics

Newton's Laws Concepts
Concept chapter for Newton's Laws in PDF format

Newton's Laws Practice Items
Problem set for Newton's Laws in PDF format

Answer Key
Answers and explanations

Newton's Laws Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Dynamics
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Be able to clearly recall and express Newton's Laws of Motion in plain English.

Pay special attention to Newton's Second Law, understanding the basic relationship between force interactions and changes in an object's state of motion.

Move beyond the traditional 'contact forces' of mechanics to include an understanding of the classical fundamental forces and their relationship to Newton's Laws. Be able to compare and contrast the gravitational force and the electrostatic force.

Be able to distinguish mass and weight.

Become comfortable solving problems involving kinetic and static friction.

Understand how to construct free body diagrams, especially for classic model problems such as the inclined plane, the elevator, and objects suspended from multiple cables.

Understand at a basic level how the orientation of the forces on an object and the position of its center of mass determines a mix of translational and rotational dynamics.

Suggested Assignments

Warm up with a question drill for dynamics conceptual vocabulary. To make sure you have the basic vocabulary down try to complete the fundamental terms crossword puzzle without pausing. Here is the solution to the puzzle.

Study the physics cards for Newton's laws.

Study the WikiPremed Newton's laws chapter. Perform the kinematics practice items. Here is the answer key for the problem set.

In ExamKrackers Physics, read pp. 20-27 and pp. 31-37. Perform practice items 17-24 on pg. 28 and 25-32 on pp. 38-39.

Finish your main progression work on dynamics with a review tour of the web resources suggested at the subtopic level within the science outlines on this site. HyperPhysics is highly recommended, as are the PY105 notes. The Monterey multimedia presentations are excellent, especially if physics has not been a strength in the past.

Conceptual Vocabulary for Dynamics

Force is anything that can cause a massive body to accelerate. It may be experienced as a lift, a push, or a pull.
Mass is a fundamental concept in physics, roughly corresponding to the intuitive idea of how much matter there is in an object.
Dynamics is the branch of classical mechanics that is concerned with the effects of forces on the motion of objects.
Isaac Newton
Sir Isaac Newton was an English scientist whose treatise Philosophiae Naturalis Principia Mathematica, published in 1687, described universal gravitation and the three laws of motion.
Galileo Galilei
Galileo Galilei was an Italian physicist, mathematician, astronomer, and philosopher who achieved the first systematic studies of uniformly accelerated motion, improved the telescope and supported Copernicanism.
Weight is a measurement of the gravitational force acting on an object.
Newton's laws of motion
Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and its movement through space.
Centripetal force
The centripetal force is the external force required to make a body follow a circular path at constant speed. The force is directed inward, toward the center of the circle.
Friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact.
Coefficient of friction
The coefficient of friction is a dimensionless quantity used to calculate the force of friction (static or kinetic).
Normal force
The normal force is the component, perpendicular to the surface of contact, of the contact force exerted by the surface.
Contact force
A contact force is a force between two objects that are touching each other.
The newton is the SI derived unit of force.
Inertia is the property of an object to remain at constant velocity unless acted upon by an outside force.
Net force
A resultant or net force is a vector produced when two or more forces act upon a single object.
Newton's third law states that forces occur in pairs, one called the action and the other the reaction.
Fundamental interaction
A fundamental force or interaction is a mechanism by which particles interact with each other and which cannot be explained in terms of another interaction.
Sliding friction
Sliding friction is when two solid surfaces slide against each other.
Inertial frame of reference
An inertial frame of reference is one in which Newton's first and second laws of motion are valid, ie. that is neither rotating nor accelerated.
Tension is a reaction force applied by a stretched string, rope or a similar object, upon the objects which stretch it.
Rolling resistance
Rolling resistance is the frictional resistance that occurs when an object rolls. It is usually much smaller than sliding friction.
The dyne is a unit of force specified in the centimeter-gram-second (cgs) system of units.
Fictitious force
A fictitious force is an apparent force that acts on all masses in a non-inertial frame of reference arising from the acceleration of the non-inertial reference frame itself.

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