CH 4-5-6 Flashcards
What weighs 1 N?
an apple
What weighs 10N?
Large Textbook (a 1 liter bottle of soda)
What weighs 100N?
3 Gallons of milk
What weighs 1000N?
Mr. Nystrom wearing a backpack full of books
If you weigh 600N and are hanging on a rope, you are pulling down 600N on the rope. The rope is pulling ______
up 600N on you!
If you weigh 600N and jump off of a building, do you accelerate towards the earth? Does the earth accelerate towards you?
YES, you accelerate toward the earth and YES the earth accelerates toward you (it is hard to see)
How can you think of gravity to help you “see” objects being pulled towards eachother?
Imagine a bungee between them. A bungee between two cars may pull them both together at the same acceleration, but a bungee between a car and a skateboard will mostly pull the skateboard more. MASS RESISTS ACCELERATION
Why don’t you see the earth move when you jump up?
It is so massive that it barely moves
If force = mass * acceleration, then acceleration =
FORCE / MASS
if force = mass * acceleration, then mass=
FORCE / ACCELERATION
When you fire a gun, the force on the bullet is equal to the _____________
force on the gun
why does a bullet go faster forward than the gun moves backwards if they have the same force?
the gun has more mass. If you push a roller skate with the same force that you push a bus, the rollerskate will accelerate faster! Mass resists acceleration.
What is a way to think of mass when it comes to movement?
MASS RESISTS ACCELERATION (this is what we call inertia)
How do you sketch the resultant force of two vectors?
USE THE PARALELLOGRAM RULE.
What does the delta (the little triangle) symbol mean?
It means “CHANGE IN”
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?
F= ma 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: harder to push more massive objects , 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
It is what is left after you combine all the forces (things cancel out).
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 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 (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!
block on inclined plane: What is Fd and FN?
Fd is directional force DIAGONAL down plane along the slope, FN is normal force directly into the plane
Explain what Fd is in plain terms
Directional force, it is the force that acts on the block pushing it down the ramp. it goes diagonally down the ramp, parallel to the ramp.
Explain Fn in plain terms
It is the squeeze force between the block and the ramp. It measures the force going directly perpendicular into the plane. It is in the direction of an upside down thumb tack.
How can remember the direction of the normal force?
a thumb tack on its back. the pointy side is in the direction of the normal force.
Directional force (down along the plane) is:
Fd
It is directional, or down the plane, parallel to the plane, along the plane
The force between the block and the ramp is
the normal force, Fn (the squeeze force)
If you have weight, how do you find normal force?
w*cos (angle) gives normal force. “COS it’s normal”
If you have weight, how do you find directional force?
w*sin(angle) gives the directional force. “SINES GIVE DIRECTIONS”
What do we use normal force to calculate?
FRICTION. it is the squeeze force since it is the measure of the force between the block and the plane, it determines amount of friction. Friction=FN * Mu
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 is a NEWTON a unit for?
for FORCE and WEIGHT (weight is a force)
What are the units in a NEWTON?
kg*m/s2 (notice it it a mass * acceleration)
what are the units we use for acceleration?
m/s2
What are the units we use for mass?
kg
a newton (F) divided by acceleration (a) (m/s2) will give you
mass (kg)
a newton (F) divided by a mass (m) (kg) will give you
an acceleration (m/s2)
a mass (m)(kg) multiplied by an acceleration(a) (m/s2) will give you
a newton (force)
is mass a force? explain
No. to be a force you need a mass AND acceleration. Mass is a scalar quantity and has no direction. Force is a vector.
is weight a force? explain
YES. F=ma, W=mg. gravity is an acceleration, so when you do mass times gravity, that is the same as mass times acceleration.
How much does a 3kg object weigh?
about 30N
Is acceleration scalar or vector?
vector (has direction and magnitude)
What is the mass of a 35N object?
3.5 kg
What is acceleration when 12N is applied to 3kg object? Why?
4 m/s2. Since F=ma, then a=F/m so 12N/3kg = 4m/s2
What is the net force on a 10kg object that is accelerating at 2 m/s2
F = ma so 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 30/ 5 = 6kg
What force do you need to accelerate a 1000kg car 5 m/s2 ? (ignore friction)
5000N
What will the acceleration be of an 800kg car that is pushed with a force of 8000N? (ignore friction)
10m/s2
What is terminal velocity?
the highest 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, mass is a measure of resistance to change, weight is the force due to gravity on the planet it is on
Which is more stable, mass or weight? Explain
mass is same on earth or moon, weight changes on different planets with diff gravity. Also, you weigh less on a plane than on the ground (gravity decreases the further from earth you are)
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 (things at rest or motion stay that way)
Give an example of Newton’s second law in real life:
harder to push a car than to push a skate board (mass resists acceleration, f=ma)
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 (equal and opposite)
Do you weigh more on the ground or in an airplane?
On the ground. The further from an object, the less its gravitational pull influences you.
An object in equilibrium is
standing still or moving at a constant velocity.
if there is a net force then the object must be
accelerating.
if an object is moving, must there be a force on it?
NO. it can be moving at a constant velocity with no force, if it’s velocity changes, then there must be a force present.
A 60N object has a _________
mass of 6kg
A 55kg object has a _______
weight of 550N
2.5N= ___kg
.25kg
2.5kg=___N
25N
if a force acts in the same direction as the velocity, then the object will
speed up (positive acceleration)
if a force acts in the opposite direction as the velocity then the object will
slow down (negative acceleration, or deceleration)
what is terminal velocity?
when the force of air resistance is equal to the weight ( weight is the force due to gravity). It is in equilibrium.
what happens when an object reaches terminal velocity?
It stops accelerating. It has reached its top speed and it just continues down at a constant velocity.
What is the net force of an object moving at its terminal velocity?
zero. No acceleration.
If something is slowing down, then it is accelerating in the ________ direction
opposite.
If something is speeding up, then it is accelerating in the ____ direction,
same
if a problem says “constant velocity” that means that the acceleration is ____ and the net force is _____
the acceleration is zero and the net force is zero.
