Chapter 4 Physics: Newton's Second Law

What is force?

any push or pull exerted on an object, measured in newtons

What is friction?

the resistive force that opposes the motion or attempted motion of an object either past another object with which it is in contact or through a fluid

What is mass?

the quantity of matter in an object. More specifically, it is the measure of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, deflect it, or change in any way its state of motion

What is weight?

the force upon an object due to gravity, mg (more generally, the force that an object exerts on a means of support

What is volume?

the quantity of space an object occupies

What is Newton’s second law?

the acceleration of an object is directly proportional to the net force acing on the object, is in the direction of the net force, and is inversely proportional to the mass of the object

What is free fall?

motion under the influence of gravitational pull only

What is terminal speed?

the speed at which the acceleration of a falling object terminates because air resistance balances gravitational force

What is terminal velocity?

terminal speed with direction specified

When does an object move at constant velocity?

when no unbalanced forces act on it

What causes an object to accelerate?

unbalanced forces acting on an object

What is net force?

the combination of forces acting on an object

What kind of force does acceleration depend on?

net force

Is applied force the only force acting on an object?

no, other forces may act as well

How do you increase the acceleration of an object?

you must increase the net force acting on it

What happens if you double the net force on an object?

acceleration doubles

What is the relationship between an object’s acceleration and the net force acting on it?

it is directly proportional (written acceleration ~net force)

What causes friction?

the irregularities in the surfaces in mutual contact, and it depends on the kinds of material, and how much they are pressed together

In what direction is friction?

always in the direction that opposes motion (if an object slides down an incline, it experiences friction in the up direction; if an object slides to the right, friction goes towards the left)

If an object is to move at a constant velocity what needs to cancel?

a force equal to the opposing force of friction must be applied so that the two forces exactly cancel each other (results in 0 acceleration and constant velocity)

What the difference between static friction and sliding friction for given surfaces?

static friction is somewhat greater than sliding friction (example: it takes more force to get it going than to keep it sliding)

What does the force of friction not depend on?

speed and the area of contact

What is friction not restricted to and where else does it occur?

solids sliding or tending to slide over one another and can also occur in liquids and gases (both of which are called fluids)

When does fluid friction occur?

as an object pushes aside the fluid it is moving though

What does the friction of fluids depend on?

the speed (meaning it is appreciable even at low speeds)

What is air resistance (or air drag)?

a common form of fluid friction for something moving through air

What does the amount of inertia depend on?

the amount of matter in the object (more matter=more inertia or the greater the mass= greater the inertia)

Can an object have a weight even if gravity is not a factor?

yes (for example in a rotating space station)

In the absence of acceleration (and near the Earth’s surface) what is the relationship between mass and weight?

they are directly proportional to each other (for example: if mass is doubled, weight is doubled)

What is the measure of matter?

expressed in a mass unit (kilogram)

What is the unit of force?

newton (N)

What does a 1 kg brick weigh?

10 newtons

Does mass ever change?

no, it is the same everywhere

If a 1 kg brick is on a planet with a stronger gravity what would it weigh (in general)?

it would weigh more

What is the difficulty of lifting something against gravity?

weight

Is volume a good indication of mass?

no (volume only describes how big an object is)

What is the relationship between acceleration and mass?

they are inversely proportional (acceleration ~ 1/mass) meaning if one doubles, the other halves

What is the equation for acceleration using Newton’s second law?

acceleration= net force/mass (a=Fnet/m)

Where is the direction of acceleration?

always in the direction of the net force

What will increase an object’s speed?

applied force in the direction of the object’s motion

What will decrease an object’s speed?

applied force in the opposite direction

What will a force applied at a right angle do?

deflect the object

What will result in a combination of speed change and deflection?

any other direction of application

What does an acceleration of an object depend on during free fall?

not only force but the object’s resistance to motion (inertia)

Force produces what and inertia resists what?

force produces acceleration, inertia resists it

Formula for weight

W=mg

Formula for gravity using force and mass

g=F/m

What 2 times the force exerted on an object with twice the inertia has the same acceleration?

an object with half the inertia and half the inertia

When is net force less than the force due to gravity?

when there is air resistance

What does the force of air drag depend on?

the speed of the falling object and the size of the object (frontal area)

How is a lower terminal velocity obtained?

spreading oneself out

Terminal velocity is greater for who?

a heavier person