Chapter 3 - Dynamics Flashcards
Define “force”
An influence which changes, or tries to change, the state of motion of a body or the shape or size of a body
What is the Sl unit for force?
Newton (N)
Define “mass”
A measure of the amount of matter in a body (or object)
What is the SI unit for mass?
kilogram (kg)
What is used to measure mass?
electronic balance, beam balance
Define “gravitational field”
A region in which a mass experiences a force due to gravitational attraction
Define “gravitational field strength”
The gravitational force (in N) acting on a unit mass
Gravitational field strength is measured in ________
N kg^-1
Gravitational acceleration / acceleration due to gravity is measured in ________
m s^-2
Formula to calculate weight
W = mg
[ weight (gravitational force) = mass x gravitational acceleration ]
Similarity between mass and weight
Both are physical quantities
Differences between mass and weight (5)
- Mass is a measure of the amount of substance in a body whereas weight is due to the gravitational force on a body
- Mass is a scalar whereas weight is a vector
- SI unit for mass is kg whereas SI unit for weight is N
- Mass is constant regardless of the gravitational field strength whereas weight varies according to the gravitational field strength
- Mass is usually measured by a beam/electronic balance whereas weight is measured by a spring/compression balance
Define “friction”
A force that exists between two surfaces when at least one is rough
Friction opposes ________ between two surfaces in contact
relative motion
Friction ________ with applied force until maximum value (________ friction)
increases
limiting
Friction is proportional to the ________ from the surface in contact
normal contact force
Friction is zero when there is ________ applied even if one of the surfaces is rough
no force
Friction is zero when surfaces are ________ even if a normal contact force is applied and/or object is moving
smooth
Friction can be greatly reduced by the use of ________ on a surface
lubricants
Define “tension”
A force which acts through a stretched rope/string/cable
Define “normal contact force”
A force that is perpendicular to the surface of contact
Define “upthrust”
An upward force exerted by a fluid (liquid/gas) on an object (fully or partially) immersed in the fluid
Upthrust opposes ________
the object’s weight
If an object floats, upthrust is ________ than weight
greater
Define “density”
The mass per unit volume
Formula to calculate density
m/v
[ mass / volume ]
Formula to calculate average density (for a mixture of substances)
total mass / total volume
What is the density of water
1.0g cm^-3
= 1000kg m^-3
An object stays at rest even when force is applied due to ________
static friction
There is no resultant force → forces acting on an object are ________
balanced
There is a resultant force → forces acting on an object are ________
unbalanced
Define “resultant force”
The sum of forces acting on an object
State Newton’s First Law of Motion
An object at rest will remain at rest and an object in motion will continue in motion at constant speed in a straight line unless a resultant force acts on it
Define “inertia”
A body’s tendency to continue with its state of rest or motion
The mass of a body is a measure of its ________
inertia
The greater the mass of a body, the ________ its inertia
greater
State Newton’s Second Law of Motion
The resultant force acting upon an object is equal to the product of the mass and the acceleration of the object; the direction of the force is the same as that of the object’s acceleration
Formula to calculate resultant force
F = ma
[ resultant force = mass x acceleration ]
When an object falls vertically through air, the upward resistive force R (air resistance or drag force) acting on it ________ as the velocity of the object increases
increases
The object will fall with terminal velocity when…
the downward force of gravity (weight) on the object is equal to the upward resistive force R on the object
Terminal velocity is the ________ velocity of the object
constant maximum
State Newton’s Third Law of Motion
The force which body A exerts on body B is always equal in magnitude and opposite in direction to the force which body B exerts on body A
Forces always occur in pairs called ________ and ________ forces
action
reaction
Each pair of action-reaction forces are always… (4)
- equal in magnitude
- opposite in direction
- acting on different bodies
- of the same nature
When force F is resolved into two components P and Q,
P (the vertical force) = ________
Q (the horizontal force) = ________
F sin θ
F cos θ
