Force and Motion, Gravitation Flashcards
The center of mass
The center of mass is the average distance, weighted by mass
Newton’s first law, inertia
The law of inertia basically states the following: without an external force acting on an object, nothing will change about that object in terms of speed and direction.
Newton’s second law
Net force = mass * acceleration
Units of a Newton
N = kg·m/s2
Newton’s third law
Every action has an equal and opposite reaction. That’s why rockets work in space.
Law of Gravitation
Compare the strength of gravitational force to electric force and how you know which is stronger.
- Gravity is the weakest of the four universal forces.
- This weakness is reflected in the universal gravitational constant, G, which is orders of magnitude smaller than the Coulomb’s constant.
Acceleration of Uniform Circular Motion
Force of Uniform Circular Motion
Circumference of Uniform Circular Motion
Arc of Uniform Circular Motion
Sector of Uniform Circular Motion
What is the direction of uniform circular motion?
The direction of both the acceleration and the force is toward the center of the circle.
What is weight?
Weight is the force that acts on a mass
What is the weight at the surface of the earth?
W = mg
What do you weigh on an elevator going up?
W = mg + ma
What do you weigh on an elevator going down?
W = mg - ma
When something is laying still on a horizontal plane, what is the normal force equal to?
When something is laying still on a horizontal surface, the normal force is equal and opposite to the weight.
When something is laying still on an inclined plane, what is the normal force equal to?
When something is laying still on an inclined plane, the normal force and friction force adds up in a vector fashion to equal the weight.
What is friction?
Friction is a force that is always in the direction to impede the sliding of surfaces.
What are the equations of static and kinetic friction?
Static Friction:
Kinetic Friction:
What is the difference between static and kinetic friction?
- Static friction pertains to objects sitting still. An object can sit still on an inclined plane because of static friction.
- Kinetic friction pertains to objects in motion. A key sliding across the table eventually comes to a stop because of kinetic friction.
What is the direction of the friction vector?
Always opposite the motion of the surface involved
Motion on an inclined plane
On an inclined plane, what does the normal force do?
To prevent the object from crashing through the surface of the inclined plane, the surface provides a normal force that is equal and opposite to the normal component of gravity.
In an object that begins to slip on the inclined plane, what is the parallel component in relation to static friction
parallel component of gravity > static friction.
In an object that accelerates down the inclined plane, what is the parallel component of gravity in relation to friction
parallel component of gravity > kinetic friction.
When you push an object up an inclined plane, what do you need to overcome?
you need to overcome both the parallel component of gravity and friction.
What is the purpose of pulleys on a system?
Pulleys reduce the force you need to lift an object. The catch - it increases the required pulling distance.
What are the four forces?
- The strong force: also called the nuclear force. It is the strongest of all four forces, but it only acts at subatomic distances. It binds nucleons together.
- Electromagnetic force: about one order of magnitude weaker than the strong force, but it can act at observable distances. Binds atoms together. Allows magnets to stick to your refrigerators. It is responsible for the fact that you are not falling through your chair right now (MCAT people love to throw you quirky examples like this one).
- Weak force: roughly 10 orders of magnitude weaker than the strong force. Responsible for radioactive decay.
- Gravity: roughly 50 orders of magnitude weaker than the strong force. Responsible for weight (not mass!). Also, responsible for planet orbits.
Given a number of ropes contributing to a pulley, n, how much force do you have input to move the mass m?
You have to input: m / n
