Flashcards in C5 Terms Deck (72):
A push or pull on a system. Can either be scalar or vector.
The SI unit of force.
Strong nuclear force
The force that holds protons and neutrons together in nuclei.
The attractive or repulsive force produced by static and moving charges in atoms.
weak nuclear force
A force exerted between elementary particles of matter within the nucleons
gravitational force (Fg)
The force exerted by all matter on other matter.
The force that acts between systems when one system touches another.
List four mechanical (contact) forces
Compression - drill pressTension - dog on leash pullingTorsion - twisting lid off bottleShear - shear pins
How is dynamics different from kinematics?
Dynamics is the sudy of how forces affect an objects motion, and kinematics is the science of discribing how things move.
What kind of physical quantity is a force?
A vector quantity.
What is the SI unit of force?
What symbol for force is used in diagrams?
What 2 symbols are used for force in formulas?
F or an f with an arrow on top.
Compare contact and field forces
Contact forces are exerted by objects that are in contact with each other. Field forces act across distances without physical contact.
Which fundamental force is responsible for holding the universe’s matter in recognizable structures such as planets?
If forces acting on a system produce a net force, what can we say about those forces?
They are unbalanced forces.
What is the mathematical relationship between weight and mass of an object?
What restriction exists in using 9.81 N/kg as the proportionality constant for determining weight?
It has to be near the Earths surface.
(T/F) Compressive and tensional forces act in opposite directions on a system?
The mathematical description of a field force exerted in the space surrounding an object that is the source of or is susceptible to the field force.
A non contact force exerted on a susceptible object by similar objects.
Do all field forces visibly affect all matter?
No, some materials are susceptible to certain field forces, and others are not. (Electric and magnetic forces for example) All materials are affected by a gravitational field.
A force that in combination with other forces acting on the same system produces a zero net force on the system.
A force exerted on a system by something in its surroundings.
The single unbalanced force acting on a system that is the sum of all forces acting on the system.
A force that in combination with other forces acting on the same system results in a nonzero net force and produces a change in motion of the system.
The tendency of all matter to resist change in motion.
What is the physical property of inertia?
Laws of motion
Written by Newton and define the science of dynamics and apply to all areas of mechanics.
law of inertia (Newton's first law)
A law stating that objects at rest remain at rest and objects in motion continue in a straight line at a constant velocity unless acted upon by a net external force.
The condition in which all forces acting on a system are balanced as indicated by the system's lack of acceleration.
Law of accelerated motion (Newton's second law)
Law stating that the acceleration of a system is directly proportional to the net force acting on the system and is inversely proportional to the system's mass. F = m*a
action–reaction principle (Newton's third law)
Law stating that for every force exerted on a system by its surroundings, the system exerts an equal but opposite force.
According to Newton’s 3rd law, if you exert 20N of force kneading bread, what else must be true.
The bread is exerting 20N force on you.
A contact force that opposes the movement of objects past each other.
The force exerted by a supporting surface on a object resting on it.
The lack of what technology hampered the early studies of dynamics?
How is mechanical equilibrum defined by Newton's 1st law different from the 2nd law of motion?
Mechanical Equilibrum is when there is no net force on an object. Newton's second law shows how the motion of an object changes when the net force is not zero.
Describe what is meant by a "force" in Newton's 2nd law of motion?
Its the magnitude of the net force acting on the system in newtons.
When you stand on a sidewalk, your weight is exerted on the sidewalk. According to Newton's 3rd law, what does the sidewalk do? Why do you not experience any vertical motion while standing on the sidewalk?
It push up on you. The forces are equal.
Why do you suppose engineers chose to use tension forces to pull up elevators rather than compression forces to push them up?
Because they can use a weight to pull it up and save alot of energy.
A bat exerts an unbalanced force on a softball, and the ball exerts the same foce in the opposit direction on the bat. Which force accelereates the softball out of the park? Justify your answer by identifying the system of interest?
The bat. The bat is the origin of the force.
How is friction related to Newton's 3rd law of motion?
It opposes an opposite force to movement.
How does static fricition between 2 stationary systems touching each other compare to the kinetic friction when they are sliding past each other?
Static friction is greater than Kinetic friction.
(T/F) An object will accelerate whenever there is an external force exerted on it.
Law of universal gravitation
Law stating that the force of gravity between two objects is directly proportional to the products of their masses and inversely proportional to the square of the distance between their centers of mass. Fg=G*(Mass 1 * Mass 2) / r2
gravitational acceleration (g)
The acceleration of an object due to gravity. At the earth's surface its average magnitude is about 9.81 m/s/s, regardless of the object's mass.
The acceleration of an object accelerated by the force of gravity alone with no other forces acting on it.
A constant acceleration, such as that of an object in free fall.
A form of friction exerted by a fluid on an object moving in reaction to the fluid.
The maximum constant speed of an object falling in the atmosphere.
What 3 variable factors determine the force of gravity between any two objects?
masses of the two objects, distance between their centers
Gravitational force (Fg) is ___________ proportional to the product of the masses, and ____________ proportional to the square of the distance between the masses.
Universal gravitation constant
1 of 4 fundamental constants of physics. Converts the measured quantities of mass and distance into the observed gravitational force between the objects.
Under what conditions is an object in free fall?
When it is dropping due to gravity with no other forces acting on it.
Can free fall be achieved near the earth’s surface?
No, due to air resistance.
w = mass (m)* gravitational acceleration (g) is the formula for what?
On what physical property does the weight of an object depend?
An object’s weight depends on its mass. Weight is directly proportional to mass.
How is the formula for weight an expression of Newton’s 2nd law (F = mass * acceleration)
Weight is a force (F) = mass * acceleration (G which is the known acceleration rate of gravity)
How does the distance an object falls in free fall relate mathematically to the time it has fallen?
It is proportional to the square of the time it has fallen. (Figure 5-26)
How does drag reduce acceleration of a falling object?
As a falling object accelerates the drag forces increases. This opposes the gravitational force (weight) of the object. The unbalanced net force on the object decreases, reducing the acceleration. When drag force = weight, the unbalanced force is zero and acceleration is zero.
(T/F) An object released from rest will fall half as fast as an object twice as heavy dropped at the same time.
False. This is the error that Aristotle made. Objects fall at the same rate regardless of mass if drag is ignored.
A property of a moving object directly proportional to its mass and speed
linear momentum (p)
The momentum of a system moving in a straight line; a quantity equal to the product of the system's mass and velocity.
The momentum of a rotating system, proportional to the mass of the system, the speed at which it rotates, and the direction of the mass in relation to the axis of rotation.
The change of a system's momentum, directly proportional to the force exerted and the time interval over which the force is applied.
conservation of momentum
A fundamental conservation law of mechanics stating that in a system of colliding objects, the sum of their momentums before the collision is equal to the sum of their momentums afterward if no external force acts upon the objects.
Two properties that affect an object’s momentum are:
Mass, speed (or velocity)
Velocity affects _____________ and ____________ of an object’s momentum.
magnitude, direction of the momentum vector
3 factors of angular momentum are:
object’s speed of rotation, it’s mass, the distance of its mass from the axis of rotation.
What important physical principle is demonstrated every time a collision occurs (when no external force)?
conservation of momentum