Chapter 6: Forces Flashcards
What happens when two forces act in the same direction
Their strengths are added
The greater the mass of an object has what effect on its inertia
its inertia is greater
The force of gravity on a person or object on the surface of a planet is
called
weight
The force that one surface exerts on another when the two rub against
each other is called
friction
Forces can be added together only if they are
acting on the same object
Gravity will pull a pencil down with the same force as a feather with the
same mass. This is an example of
Newton’s second law of motion
According to Newton’s third law of motion, when a hammer strikes and
exerts force on a nail, the nail
exerts an equal and opposite force on the hammer
If you drop a sheet of paper horizontal to the floor and a crumpled ball of
paper at the same time from the same height in your classroom, the
crumpled ball of paper will hit the floor first because
air friction has a greater effect on the sheet of paper dropped
horizontally
An object that orbits another object in space is called a(n)
satellite
How can you increase the momentum of an object
by increasing its mass
The overall force on an object after all the forces are added together is called the
____________ force
net
One ________ is the force required to accelerate 1 kilogram of mass at 1
meter per second per second
Newton
The force of gravity between you and Earth is greater than the force of gravity between you
and a car because Earth has more ____________________ than the car
mass
According to Newton’s third law of motion, the strength of a reaction force is
________ __ the strength of the action force.
equal to
The force of gravity is responsible for continuously changing the _________ in
which a satellite moves
direction
True or False: When the only force acting on a falling object is air resistance, the object
is said to be in free fall
False: Gravity
True or False: The property of matter that resists a change in motion is called inertia
True
True or False: To calculate the density of an object, you multiply mass by volume
False: divide
True or False: Friction depends on the types of surfaces involved and how hard the
surfaces push together
True
The theory of gravity describes the attraction between all objects in the
universe
False: law
How do you calculate acceleration
Final Speed-Initial Speed/Time
Why don’t action-reaction forces cancel out
. Forces may cancel out only if they are acting on the same object. Action and reaction forces act on different
objects. For example, when a person kicks a ball, the action force is on the ball but the reaction force is on the person’s foot. Therefore, the forces cannot cancel
A book is sitting on the dashboard of a car that is stopped at a traffic light. As the car starts to
move forward, the book slides backward off the dashboard. Use the term inertia to explain
what happened
When the car is stopped at the traffic light, the dashboard (which is part of the car) and the book are both at rest. As the car accelerates forward, the dashboard moves forward. But no force is exerted directly on the book, so it remains at rest. Because of its inertia, the book does not move forward when the dashboard moves forward. From the reference point of the car, the book appears to move backward, sliding off the dashboard
A skydiver with a mass of 70 kg accelerates to Earth at a rate of 9.8 m/s2 due to gravity.
What is the force on the skydiver
. Force = Mass x Acceleration =
70 kg x 9.8 m/s2 = 686 kg x m/s2 = 686 N. According to Newton’s second law of motion, force equals mass times acceleration. In this case, the mass of the person and the
acceleration due to gravity are given. Since 1 N = 1 kg x m/s2, the final unit is the newton
A block of wood is at rest on a wooden ramp. When wheels are attached to the block of
wood, it moves down the ramp. Explain each situation in terms of friction
Without wheels, the force of sliding friction balances the gravitational force pulling the block down the ramp. There is no net force on the block, so it does not slide down the incline. When wheels are attached, the force of rolling friction is much smaller than the force of sliding friction. The gravitational force
pulling the block down the ramp is now greater than the friction force between the block and the ramp. Therefore, there is a net force on the block pulling the block down the ramp, so the block begins to move in the direction of this unbalanced force
When you know both the speed and direction of an object’s motion, you
know the
velocity
What is the SI unit of acceleration
m/s2
An object changing direction is an example of
acceleration
What is acceleration
The rate at which velocity changes (speed and direction)
What is a force
A push or pull exerted on an object
What is the newton
A unit of measure that equals the force required to accelerate 1 kilogram of mass at 1 meter per second
What is net force
The overall force on an object when all the individual forces acting on it are added together
What is friction
The force that two surfaces exert on each other when they rub against each other
What is sliding friction
friction that occurs when one solid surface slides over another
What is static friction
Friction that acts between object that are not moving
What is fluid friction
Friction that occurs as an object moves through a fluid
What is rolling friction
Friction that occurs when an object rolls over a surface
What is gravity
The attractive force between objects; the force that moves objects downhill
What is mass
A measure of how much matter is in an object
What is weight
A measure of the force of gravity acting on an object
What is inertia
The tendency of an object to resist a change in motion
What is momentum
The product of an object’s mass and velocity
What is the law of conservation of momentum
The rule that in the absence of outside forces the total momentum of objects that interact doesn’t change
What is free fall
The motion of a falling object when the only force acting on it is gravity
What is a satellite
Any object that orbits another object in space (usually a planet)
What is centripetal force
A force that causes an object to move in a circle
What is the SI unit of acceleration
m/s2
What is the SI unit of force
Newton (kg*m/s = N)
What are the two factors that affect friction
type of surface and how hard the objects are pushed together
What is the law of universal gravitation
The force of gravity acts between all objects in the universe that have mass
What are the two factors that affect the gravitational attraction between objects
mass and distance (more mass = more gravity, more distance + less gravity)
What is the SI unit of mass
the kilogram
What is Newton’s first law
The law of inertia: an object at rest will remain at rest unless acted upon by a nonzero net force. An object moving at constant velocity will continue moving at a constant velocity unless acted upon by a nonzero net force
What is newton’s second law
an object’s acceleration depends on its mass and on the net force acting on it
How do you calculate acceleration with net force and mass
NF/M
How do you calculate Net Force
Mass*Acceleration
What is Newton’s Third Law
The law of action and reaction: if an object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object
How do you calculate momentum
Mass*Velocity
What is “quantity of motion”
momentum
How do you calculate velocity
Time*Acceleration
