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Physics Ch. 5
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Gravity
Terms in this set (16)
Force
Required to change motion
Newton's First Law
"An object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force."
Explain why Newton's first law is also known as the law of inertia
Objects tend to keep doing what they are doing or that object resist changes in their motion. Inertia is an objects ability to resist changes in its state of motion and is an important part of Newton's law
Give an example of Newton's first law in everyday life
An example of Newton's first law in everyday life is when blood rushes from your head to your feet while quickly stopping when riding on a descending elevator
Net force
Total of all the forces acting on an objects
Newton
Metric unit of force
An object with more mass also has more
Inertia
Newton's Second Law
Relates force, mass, and acceleration in the equation F=MA
Weight
The force of gravity on an object
Terminal Speed
When the force due to gravity equals the force due to air resistance, the speed of a falling object is called this
Define the term force and give three examples
Force - A push of pull or any action that has the ability to change motion
An applied force is a force that is applied to an object by a person or another object. If a person is pushing a desk across the room, then there is an applied force acting upon the object. The applied force is the force exerted on the desk by the person.
The normal force is the support force exerted upon an object that is in contact with another stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book.
The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.For example, if a book slides across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion.
Newton's Third Law
For every action force, there is a reaction force equal in strength and opposite in direction
When Jane drives to work, she always places her purse on the passenger's seat. By the time she gets to work, her purse has fallen on the floor in front of the passenger seat. One day, she asks you to explain why this happens in terms of physics. What do you say?
When Jane brakes, the brakes slow the car wheels turning and the road surface exerts a backwards force on the tires, causing the car to decelerate. The pocket book tends to continue on in a straight line (Newton's first law). If she brakes hard enough that the friction between the book and the car seat is insufficient to decelerate the book as fast as the car is decelerating, the book will slide off the seat, and gravity pulls it to the floor
You are waiting in line to use the diving board at your local pool. While watching people dive into the pool from the board, you realize that using a diving board to spring into the air before a dive is a good example of Newton's third law of motion. Explain how a diving board illustrates Newton's third law of motion
When the diver uses his / her force to depress the springboard, the springboard pushes him back with equal force
Describe how Newton's second law explains the scale readings for the trip up in the elevator (from the first floor to the second floor. Be sure to include the beginning, middle and end of this trip.
There are 2 forces acting on you. Your weight pulls down with a force of Newtons. The scale pushes up with a force of Newtons.
Since your acceleration is x m/s2 upward, Newton's Second Law says that there must be a net force pushing you upward, and the net force has a magnitude Fnet = ma. So the net force on you,
Fnet = (x kg)(x m/s2) = x Newtons (upward).
Since the net force on you is x Newtons, the upward forces and downward forces on you must cancel to leave an x Newton upward force. Therefore the scale must push on you with a force of x Newtons, and the scale must read x Newtons as the elevator accelerates upward.
Overall, the elevator starts with 0 velocity because there is no movement. As the elevator starts to ascend upward, there is a positive velocity and acceleration. And then as the elevator slows to a stop, there is 0 velocity.
Describe how Newton's second law explains the scale readings for the trip down in the elevator (from the second floor to the first floor. Be sure to include the beginning, middle and end of this trip.
The elevator (and you) accelerated for x seconds, so it is moving downward with a velocity of x m/s. It now moves with this constant downward velocity of x m/s.
There are 2 forces acting on you. Your weight pulls down with a force of x Newtons. The scale pushes up with a force of x Newtons.
Since the elevator is moving with constant velocity, your acceleration is x m/s2. Since your acceleration is x m/s2, Newton's First Law says the net force on you is x Newtons.
Since the net force on you is x Newtons, the scale must push on you with a force of x Newtons, and the scale must read x Newtons.
Overall, there is force with 0 velocity when there is no movement, towards the beginning of the trip. Towards the middle of the trip, there is negative velocity. And then the end of the trip there is 0 velocity because the elevator has stopped moving.
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