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Physics Classroom

Newton's Laws Lesson 1
11.14.11

Questions:

How can Newton's first law be used to explain motion? Because it explains why objects move or don't move.

What is Newton's first law? An object at rest stays at rest and an object in motion stays in motion with the same speed and direction unless acted upon by an unbalanced force.

In both situations, the objects have an acceleration of 0 m/s/s, meaning they will not change their speed or direction. Objects tend to keep doing what they're already doing.

How does it apply to real life? In many examples that are obvious and not necessary to list.

What is inertia? The resistance an object has to a change in its state of motion. This is in contradiction to what people used to believe: that a force was needed to keep an object moving. Galileo suggests that objects will move infinitely (seeking to return to the original height) but are stopped because of friction.

State of motion is defined as velocity. So inertia means the tendency of an object to resist changes in its velocity, and also resist accelerations.

How does friction relate to Newton's first law? Friction opposes motion when two surfaces come in contact. Thus, it is a force that brings an object to a stop.

How does mass relate to intertia? Mass is a quantity that is solely dependent upon the inertia of an object. More inertia = more mass... more mass=more inertia.

Inertia is a property that measures how difficult it is to change an object's motion.

This is (m)ass - (kg). (W)eight is force, pull of (g)ravity on a mass. (N)

W= m*g

What is an unbalanced force? Equilibrium is when the opposing forces are balanced. When there is equilibrium, there is no change in the state of motion.

Static Equilibrium - at rest, no motion Dynamic Equilibrium - constant speed In both cases the forces are balanced.

However, if forces are unbalanced, meaning won is of higher magnitude than the other, state of motion will change.

2nd: When an unbalanced forces acts an object, it will accelerate in the direction of the unbalanced force.

∑F = net force.

Summary:

Newton's first law deals with inertia. Objects tend to stay in the state of motion they are already in. More inertia means a more massive object. Friction is the force that opposes motion, and commonly the unbalanced force that acts on the object to change its state of motion (moving -> stopped).

Newton's Laws Lesson 2
11.15.11

Questions:

What is a force? A push or pull upon an object resulting from the object's interaction with another object. Interaction ends -> force no longer experienced.

What sorts of forces exist? Two broad categories:

Contact Forces -result when objects seem to physically touch each other. -Friction, Tension, Normal, Air Resistance, Applied, Spring

Action-at-a-distance Forces -Exert force without physical contact. -Gravitational, Electrical, Magnetic

How are forces measured? Forces are vectors measured with the magnitude of Newtons and a direction. Newton = 1 kg*(m/s/s)

What is Applied Force? -force applied by object or person

What is Gravity Force? -force of the earth (usually) pulling downward always

What is Normal Force? -support force exerted between surfaces.

What is Friction Force? -Force which opposes motion when two surfaces are in contact... Not always opposing

What is Air Resistance Force? -acts upon objects in the air, opposes motion of object. -Many times is negligible, other times left out because hard to mathematically predict its magnitude)

What is Tension? -Force transmitted through rope, chain, string. In direction of and along this rope, chain, string.

What is Spring Force? -force exerted by a compressed or stretched spring to the attached object. Magnitude is proportional to the amount of stretch/compression of spring.

What are the differences between Mass and Weight? -Weight: amount of pull by gravity on an object -Mass: amount of matter contained in the object

What is the difference between static and sliding fricton? -Sliding - when object slides across surface. Calculated using: **Sliding Ffrict = μ • Fnorm** µ is the symbol for coefficient of sliding friction. Dependent mostly on the nature of surfaces in contact, shows amount of attraction between objects, Normal force is multiplied by this.

Static friction - between two objects at rest (relatively speaking). Takes more force to start the motion of the object than to continue it.

What are Free-Body diagrams? Diagram of the system showing the relative magnitudes of the forces acting upon the object in a given situation.

What is net force? The vector sum of the forces acting on an object. Balanced forces = zero net force. Net forces (unbalanced) cause accelerations.

Newton's Law Lesson 3
What is Newton's second law, and how does it relate to his first law?

Newton's second law deals with the behavior of objects being acted upon by unbalanced forces, which builds on the premise of the first law. Acceleration of object is dependent on net force and mass of object - where the net force is directly proportional to the acceleration and the mass is inversely proportional to the acceleration.

Newton's second law of motion can be formally stated as follows: >> The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
 * a = Fnet / m**

How does net force relate to acceleration?

Net force is directly proportional to acceleration. That is, as net force increases, acceleration increases.

Measured in Newtons, which are units that represent the amount of force it takes to give 1 kg mass an acceleration of 1 m/s/s.

What is the big misconception about Newton's laws?

That a force is required to sustain motion. This is FALSE.

What is TRUE is that there can be no acceleration without a force.