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Physics 4
| Question | Answer |
|---|---|
| Solve Question 1 | -- |
| Solve Question 2 | -- |
| Solve Question 3 | -- |
| Solve Question 4 | -- |
| Solve Question 5 | -- |
| Solve Question 6 | -- |
| Solve Question 7 | -- |
| Solve Question 8 | -- |
| Solve Question 9 | -- |
| Solve Question 10 | -- |
| Dynamics | the study of the causes of motion. The basic causes of motion can be explained by Newton's three laws of motion. |
| Net Force | vector sum of all forces acting on an object. The magnitude and direction of the net force is determined by using the method of vector addition. Can be described as Fnet. |
| Inertia | refers to the tendency of an object to resist any change in its state of motion. Inertia is measured by measuring an object's motion. The SI unit of inertia and mass is kilogram (kg). |
| Newton's First Law of Motion | an object continues in an state of rest or in a state of motion at constant speed along a straight line, unless compelled to change that state by a net force. |
| Newton's Second Law of Motion | this second law refers to an object in motion when a net force does not equal zero. Essentially, F sum = ma. |
| Newton's Third Law of Motion | for every action (force), there is an equal and opposite reaction. When object A exerts a force on object B, object B simultaneously exerts a force of the same magnitude in the opposite direction. |
| Tip about Newton's Third Law of Motion | The action and reaction force are equal and opposite, but do not act on the same object. They act on two different ones. |
| Weight | the force of gravity on an object. The weight varies slightly from place to place on the surface of the earth. The variation is so small that the weight of an object located close to earth's surface is considered to be a constant. |
| Normal Force | a contact force that acts perpendicular to the common surface of contact. For example, a book at rest on a horizontal table is acted upon by two forces; the book's weight which is directed downward and the normal force that is directed upwards. |
| Tip about Normal Force | normal = perpendicular. Also remember that normal force requires contact with a surface. If there is no contact, no force. |
| Why Does the Tablecloth Pull Work | The tablecloth trick works because of inertia and the small amount of friction when the tablecloth is pulled fast enough — when the cloth is pulled quickly, friction doesn’t have time to move the dishes, so they stay (almost) in place. |
| Common Misconception about Action & Reaction Forces | People assume that weight is the reaction force to the Nor force, often not true. When they are both acting on the same object, weight is just acting down and normal force is acting up. MEANWHILE, action-reaction forces are between 2 different objects. |
| Example of FN Reaction & Action Forces | FN: the normal force is the force of the table on the block. The reaction force to FN is the force of the block on the table. |
| Tip about String Mass | The string is often going to be massless, so you can reduce it and have it still not affect anything. |
| Tip about Tension Problems | if you run into a question with two or more masses, you should first combine all the masses and solve for acceleration. Then, find all the forces acting on a single system and solve for whatever you need -- usually tension. |
| Tip about Scales | The weight shown on the scale is the true weight -> this is not correct because the number on the scale tends to fluctuate and it is closer to the force of the body on the scale. The scale reading can actually be found by solving for normal force. |
| Tip about Elevators | When the elevator moves at constant velocity, the scale reading is the same as the true weight (mg). This will also be the case when the elevator is at rest and not moving because in both cases a = 0. |
| Tip about Elevators & Person | When the elevator is moving up but accelerating, the person will feel heavier. When they're moving down but decelerating, the person will feel lighter. |
| How To Determine Direction | If the m2g is larger than the m1gsin(0), then the system will move clockwise. If the opposite is true, counterclockwise. |
| Friction | A contact force that opposes the relative motion of two surfaces as they slide past each other. The force is overcome friction when the object is initially at rest is greater than when the object is moving. |
| Coefficient of Friction | A pure number without physical units. When the surface is rough, the coefficient of friction is large. When the surface is smooth, the coefficient of friction is small. |
| Static Friction | When an object is at rest, the coefficient of static friction is used to determine the magnitude of the frictional force just before the object starts to move. |
| fsMAX | The maximum value of static frictional force is proportional to the coefficient of static friction and also to the normal force (Fn) acting on the object. Happens when the man pulls hard enough to get the object to move. |
| Kinetic Friction | When the object is moving, the coefficient of kinetic friction is used and the kinetic force of friction is given by: fk = ukFn. Whether the object is accelerating or decelerating, the relationship is always expressed in the same way. |
| Static Friction Vs. Kinetic Friction | The coefficient of static friction is always larger than the coefficient of kinetic friction: us > uk. This is because it is much harder to displace an object at the beginning. When the object starts to move, it's much easier. |
Created by:
smurtab