Unit 3: Physics
What is the sigma (E) notation and how is it used?
E: sum Summing of the forces; x or y is used as subscript of the F
An object weighs 653.0 N. It is being pushed along a horizon a tal surface by a 268.0-N force. Determine the mass of the object.
Either 66.56 or 66.56 kg (?)
The force of gravity of objects on the moon is approximately one-sixth of their value on Earth. Joe weighs 600 N on earth. Joe's mass on the moon will be approximately _________.
60kg
What is a contact force?
A force that acts on objects by touching the object. Friction forces, normal forces, and forces applied by people.
What is a field force?
A force that acts on objects without touching the object. Forces like gravity, the magnetic force, and the electric force.
What is a force, conceptually?
A push or a pull by one object on another object.
How do you find the resultant force in a 2D force problem?
Break and angled forces into components. Add up all of the individual x-axis forces to find EFx. Add up all of the individual y-axis forces to find EFy. Use equation of Fnet = squareroot of (EFx)^2 + (EFy)^2 and inverse tan to find theta.
How do you find the resultant force in a 1D force problem?
Choose a sign convention (e.g., up is positive and down is negative.) Then, add up all of the individual forces exerted on the object.
What do Newton's three laws of motion do?
Connect forces with motion (velocity, acceleration)
Suppose that an astronaut throws a rock in outer space at a location far from significant influences of gravity and air resistance. One would expect that the rock would ______.
Continue in motion with the same speed and direction. Why? __________
What has the effect of increasing the acceleration of an object?
Decreasing the mass of the object. Doubling the net force experience by the object. Halving the mass of the object.
What is the friction force?
Definition: It is the force of a surface on an object, directed parallel to the surface, which opposes the object's motion.
What is the normal force?
Definition: it is the force of a surface pushing on an object, which is directed perpendicularly to the surface. Function: it is a force that supports objects and prevents them from falling through the floor.
True or False: The mass and weight of an object are the same thing.
False
True or False: The mass of an object is the force of gravity acting upon the object.
False
True or False: The weight of an object is its mass multiplied by the force of gravity.
False
True or False: The weight of an object on the moon will be the same as its weight on earth.
False
What is the variable for resultant force?
Fnet
Is force a vector or a scalar?
Force is a vector.
The more mass an object has, the _________ the object's inertia.
Greater
What is weight?
How strongly gravity pulls on your matter
What is the net force, conceptually?
If you wanted to exert just one force on an object instead of applying many individual forces, you could simply exert the resultant force, and the same acceleration would be produced.
Force diagrams:
Just show force, not which way the object is going (moving). They show which way net force/acceleration points.
When all individual forces acting on an object are balanced, it is the natural tendency of an object to _____.
Keep its velocity constant (either at a zero or non-zero value)
What is the unit of mass?
Kg
The less mass an object has, the _______ the object's inertia.
Lower
The amount of matter or "stuff" in an object is referred to as the ______ of the object.
Mass
Using Newton's Second Law, derive what 1 Newton equals (in terms of fundamental units).
N = (kg)(m/s^2)
What are other names for the net force?
Net force, resultant force (?) and total force
What is the unity of weight
Newton (N)
What is the unit of force, and what is it derived from?
Newton (N) 1N = (1kg)(m/s^2)
What is Newton's first law?
Objects at rest remain at rest. And objects in motion move at constant velocity, unless acted upon an unbalanced force. What happens when forces balance? They are constant (?)
What is mass?
The amount of matter in an object
What force does a scale measure?
The force of gravity
What is a net force?
The net force on an object is: the sum of the individual forces each exerted on the object.
A sled slides down a hill, reaches the level surface and eventually comes to a stop. The fact that the sled ultimately comes to a stop can best be explained by _______ .
The presence of an unbalanced force (e.g., friction) can cause a moving object to stop.
What is Inertia?
The property of mass to either remain at rest or continue moving in a straight line at constant speed.
Inertia refers to _________.
The tendency of moving objects to remain in motion and the tendency of stationary objects to remain at rest.
The law of inertia (Newton's first law) applies ______.
To both moving and non moving objects
True or False: On Earth, more massive objects weigh more than less massive ones.
True
True or False: The mass of an object on the moon will be the same as its mass on earth.
True
What is the formula used to calculate weight?
W = mg or Fg = mg g = +9.81m/s^2
The force of gravity that acts upon an object is referred to as the _______ of the object.
Weigh
What is Newton's Second Law?
When the forces of an object don't balance, the object accelerated according to: a = Fnet/m or Fnet = ma What happens when there's some net force? The forces don't balance. See page 11.
Can force be two-dimensional?
Yes! Any vector can be 2D.
Mass is expressed in units of ____ and weight is expressed in units of _______.
kilograms (kg), Newtons (N)
In force diagrams, the arrows are called _____ and they represent _____, because they have both ______ and _____.
vectors, forces, magnitude, direction