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Conceptual Physics - Newton's 1st and 2nd Laws

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What is Newton's First Law of Motion?
An object at rest remains at rest and an object in motion remains in motion at a constant velocity unless acted upon by a net outside force.
Inertia
- literally means lazy
- doesn't want to change their motion
- resistance to acceleration
Force
- push or pull
metric units: newtons
English units: pounds
Mass
- amount of matter in an object
- same as inertia
- independent of location
- DOESN'T CHANGE
metric unit: kilograms
English unit: slugs
Weight
- force of gravity
- depends on location
- NOT THE SAME AS MASS
metric units: newtons
English units: pounds
Equation for weight
W (weight) = M (mass) x A (acceleration of gravity)
New Force
- sum total of all forces
- forces can add or subtract
- direction matters
Just because something is moving, does not mean that _________________, It could mean that the forces are ________________.
there is no force, balanced (no net force)
Equilibrium
- forces balanced
- no net force
does NOT mean NOT MOVING, it means NOT ACCELERATING
Normal Force
The 'normal force' is the RESPONSE of a surface to a PUSH. It pushes back with EQUAL AND OPPOSITE FORCE up to some MAXIMUM.
- Normal force is caused by REPULSION OF ELECTRONS
What is Newton's Second Law of Motion?
The acceleration an object receives is directly proportional to THE NET FORCE and inversely proportional to THE MASS
- more force gives MORE ACCELERATION
- more mass gets LESS ACCELERATION
{A (acceleration) = Fn (net force)/M (mass)} {Fn (net force) = M (mass) x A (acceleration)}
Friction
- Friction is a FORCE that OPPOSES MOTION. It 'tries' to keep things from MOVING or STOPS things that are moving.
- Friction is not the same thing as INERTIA which 'tries' to keep things from ACCELERATING.
- Even if there is no FRICTION there is still INERTIA
What are the different types of friction?
1. SLIDING FRICTION
- static
- kinetic
2. ROLLING FRICTION
3. FLUID FRICTION (drag)
- water
-air
Apparent Weight
- how heavy you feel
- not the force of gravity
- force opposing gravity
- usually the normal force
Example: Elevator Ride
a. Not yet moving
Fn = FG
G = 1
- feel regular weight
Example: Elevator Ride
b. Accelerating up
Fn > Fg
G > 1
- feel heavy
Example: Elevator Ride
c. Moving at constant velocity
Fn = Fg
G = 1
- feel regular weight
Example: Elevator Ride
d. Decelerating up
Fn < Fg
G < 1
- feel light
Example: Elevator Ride
e. Cable breaks - Free-fall
Fn = 0
G = 0
- feel weightless
Example: Elevator Ride
f. Pulled down faster than Free-fall
Fn < 0
G < 0
- feel upside down
Pressure
Force/area
metric units: newtons/m2 = pascals
English units: pounds/in2 = psi
You push on a tree with 20 N of force. If the tree doesn't move, the tree is pushing back on you with ___________ of force.
20 N
If you travel to the moon, will your mass be greater than, less than, or the same as on earth?
the same as
If an object mass = 30 kg on earth, what would be it's weight on earth?
300 N
Which one needs a greater NET FORCE to move, a kilogram of feathers or a kilogram of iron?
the same
Which of Newton's laws is demonstrated by a magician pulling a tablecloth out from under dishes with disrupting them?
Newton's first law of motion
If a ball of cheese is fired into frictionless space, the amount of force needed to keep it going equals __________.
zero, since no force is required to keep it going
Which type of force(s) will cause a change in an object's motion?
Unbalanced forces
If a space explorer has a mass of 67kg but their weight is 944.7N? What planet is the explorer on?
Saturn: g=11.1 N/kg
Pluto: g=0.42 N/kg
Earth: g=9.8 N/kg
Neptune: g=14.1 N/kg
Neptune
An object will stay in what kind of motion as long as the net forces acting on it are zero?
Constant motion in a straight line
The amount that gravity pulls on you is called ___________.
Weight
Why would you weigh less on the moon than on earth?
less gravitational pull
What is the tendency of an object to resist a change in motion?
Inertia
What kind(s) of objects have inertia?
all objects with mass
Terminal velocity is ________________________.
the maximum speed an object can reach
If a 10 kg object suddenly accelerates at 15 m/s2, how much force was applied to the object?
150 Newtons
Where would you have to travel to reduce your weight but not lose any mass?
the moon
In a tug of war the left team pulls with a force of 200N. The right team pulls with a force of 150N.What is the net force?
50 N to the left
A rocket with less ________ will have a greater acceleration.
Mass
The three types of friction are?
Static, sliding, rolling
Which of Newtons laws explains why football teams have big, large, fast athletes?
Newton's Second Law of Motion
One object has twice as much mass as another object. The first object also has also twice as much...
Inertia
If the weight of a body on the Earth's surface is 600 N, what would be it's weight on moon where the acceleration due to gravity is 6 times weaker?
100 Newtons
Any change in an objects speed or direction is called ____________.
acceleration