Chap 4 and 5 Newton's Laws Flashcards
What is Newton’s First Law?
Object stays at rest, or moves at a constant velocity in a straight line unless a force acts on it.
What is Newton’s Second Law?
a= F/m Force increases acceleration, mass resists accelertion
What is Newton’s Third Law?
Every action (force) has an equal and opposite reaction
Give a quick summary of Newton’s three laws of motion:
FIRST: objects in motion or rest stay that way, SECOND: a = F/m , THIRD: action have equal opposite reactions
What are the three equations from newton’s second law? (my fish is from massachusetts)
a=F/m
F= ma
F/a = m
If you are given a force and an acceleration, you can find ____ by using the equation ____
mass,
m= F/a
If you are given a mass and an acceleration, you can find ____ by using the equation ____
Force,
F= ma
If you are given a force and a mass, you can find ____ by using the equation ____
a = F/m
Describe what NET force is
the resultant force after you consider the combination of all the forces acting on an object
How can we add two vectors (find resultant) by sketching?
Use the parallelogram rule, and the DIAGONAL is the resultant vector when both components start from the same spot.
How do we find the components if we have the resultant?
Generally, the resultant is the hypotenuse of a right triangle. So the closest side (adjacent) to the angle can be found by HYPcos(angle) and the opposite side (across) from the known angle can be found by HYPsin(angle)
How do we make sure our calculator is in the right mode?
press MODE> put cursor on DEGREES> press ENTER
What is the net force on an object at rest?
zero (not accelerating), but has potential energy!
What is the net force on an object moving at a constant velocity? Why?
zero because it is not accelerating ( but has kinetic energy!)
What has to be happening in order for net force to not be zero?
it must be ACCELERATING (changing velocity). just moving is not enough, it has to be changing speeds!
SOH CAH TOA… What do these stand for?
Sin angle= opp/hyp
cos angle= adj/hyp
tan angle= opp/ adj
block on inclined plane: What is Fd and FN?
Fd is direction of motion, force down plane along the slope, FN is normal force directly into the plane
Directional force is:
Fd is directional, or down the plane, parallel to the plane, along the plane
If you have weight, how do you find normal force?
w*cos (angle) gives normal force.
If you have weight, how do you find directional force?
w*sin(angle) gives the directional force
Normal force is:
FN is normal force, it is perpendicular to the plane (straight down into the plane). This determines amount of friction.\
The force of friction always acts____
in the opposide direction of motion
You can calculate the force of friction by multplying ____ by ____
normal force by coefficient of friction
Coefficients of friction are _____ for surfaces that are smooth and ____ for surfaces that are rough, or sticky.
smaller, larger
What is the unit of force we use?
NEWTON
What is the unit of weight we use?
NEWTON
What are the units in a NEWTON?
kg*m/s2
what are the units we use for acceleration?
m/s2
What are the units we use for mass?
kg
a newton divided by acceleration (m/s2) will give you
mass (kg)
a newton divided by a mass (kg) will give you
an acceleration (m/s2)
a mass (kg) multiplied by an acceleration (m/s2) will give you
a newton (force)
How much does a 3kg object weigh?
about 30N
Is acceleration scalar or vector?
vector (has direction and magnitude)
What is acceleration when 12N is applied to 3kg object? Why?
4 m/s2
because a=F/m
a= 12/3
What is the net force on a 10kg object that is accelerating at 2 m/s2
F = ma
so
F= 10(2) = 20N
What is the mass of an object that acceleraties 5 m/s2 when a 30N force is applied?
m= F/a
so m= 30/ 5 = 6kg
What force do you need to accelerate a 1000kg car 5 m/s2 ? (ignore friction)
F=ma so f=1000(5) = 5000N
What will the acceleration be of an 800kg car that is pushed with a force of 8000N? (ignore friction)
a=F/m so a= 8000/800 = 10m/s2
What is terminal velocity?
the greatest speed a falling object will reach because of air resistance
What is the net force on an object that is moving at its terminal velocity? Explain
zero. it is not accelerating
What receives a greater force of air resistance, an elephant or a feather falling? Why?
elephant. it is pushing through more air
What is the difference between mass and weight?
mass is the amount of stuff, weight is the force down caused by the gravitation of the planet it is on
Which is more stable, mass or weight? Explain
mass is same on earth or moon, weight changes
Give an example of Newton’s first law in real life:
an apple on a desk. net force is zero, until you push it off
Give an example of Newton’s second law in real life:
harder to push a car than to push an apple
Give an example of Newton’s third law in real life:
the floor is pushing up on you as much as you are pushing down on the floor
When a bullet leaves a gun, explain why the bullet moves faster forward than the gun moves backward
bullet has small mass, lots of acceleration,
gun has lots of mass, little acceleration
