Definitions
Friction that opposes motion once the motion has already started
What is kinetic friction?
The nucleus of atoms is held together by what force
strong nuclear force
if I have a marble and am spinning it on a disk faster and faster. What happens to the marble if I stop spinning it and don't touch the marble?
It will move straight and skid off the disc.
Pilot dropping packages as he flies east toward the target. Should he drop the package before he gets to the target, over the target, or after he passes the target?
Before the target
Write Newton's Third Law
For every action, there is an equal and opposite reaction
A force that opposes motion, resulting from the contact of two surfaces
What is friction?
In order to move a box, which force must you overcome?
Static friction
For every action force there is a
reaction force
Acceleration due to gravity changes what aspect of an object
the weight
The weakest fundamental force is
The gravitational force
Friction that opposes the initiation of motion
What is static friction?
Law of Inertia is also called
Newton's First Law
A mover pushing a sofa across the living room floor exerting a force of 300 N to keep it going at a constant velocity. What is the frictional force between the box and the ground. Is this kinetic or static friction
Even though we do not know the weight, but do know constant velocity = 0, you would use F= m x a.
M is unknown but a=0, so F=0.
This is kinetic friction because object is moving.
Write Newton's First Law
An object in motion (or at rest) will tend to stay in motion (or at rest) until acted upon by an unbalanced force.
Girl drops ball from tree and it takes 2.6 seconds for it to hit the ground. How many feet high is she?
0.5 x 32 ft/s2 x (2.6 sec)2
108.16 ft
The tendency of an object to resist changes in its velocity
What is inertia?
Your book (mass= 10kg) slides down a ramp with an acceleration of 3.0 m/s2. Ignoring friction, how much force is pulling the book down the ramp?
F=M X A
F= 10 kg x 3.0 m/s2
F= 30 N down the ramp
Write Newton's Second Law
When an oobject is acted on by one or more unbalanced forces, the total net force is equal to the mass of the object times the resulting acceleration.
In your physical science book it meantions that a book is sitting on a table. Two numbers are mentioned concerning friction. One is 15 N and the other is 20 N. Which one is static friction and which one is kinetic friction?
Static 20 N
Kinetic 15 N
Static friction is usually higher than kinetic because once an object is moving it usually has less friction.
What is the formula for finding the distance in a gravity word problem?
D= 0.5 x acceleration (32ft/s2 or 9.8m/s2) x t2
If you drop a plate and it hits the kitchen floor due to the gravitational force, what is the equal and opposite force that Newton's Third Law of motion describes?
The plate exerts an equal and opposite force on the floor
Baseball player hits a ball and his bat breaks. What is the exerting force on the bat?
The ball
Football player weighing 90kg is running towards the endzone. In order to avoid being tackled, he dives into the endzone. If the acceleration in his dive is 6.0 m/s2 into the endzone, what is the frictional force between the football plaer and the ground?
F=m x a
F = 90 kg x 6.0 m/s2
F = 540 N towards the endzone
A boy is tasked with taking the trash can to the curb for his chores. The trash can has a mass of 25 kg. The static friction between the ground and the trash can in 50 N, while the kinetic friction is 10 N. How much force must the boy exert to get the trash can moving.
He must exert over 50 N to break the static force.
Man pushes a container (m=40 kg). The static friction between the container and the ground is 30 N, while the kinetic friction is 12 N. Which what force must he push the box in order to accelerate is at 2.0m/s2 to the west?
F= m x a
F= 40kg x 2.0m/s2
F= 80 N
Net force= Force applied - Force Kinetic friction
80 N = F - 12 N
92N=F