P1- motion, forces, energy (forces, moment, pressure) Flashcards
Define force
a push, pull or twist
What can a force change
speed, direction, shape
Which type of quantity are forces
vector
What is used to show forces
arrow with heads
How does the arrow show force
- arrow size - magnitude (size) of force
- arrow head - direction of force
Note: Always label your arrows magnitude
name the 9 types of forces
-friction,
-compression
-tension
-weight
-applied
-air/ water resistance
-magnetic
-electrical
-normal (upthrust, buoyancy for in water)
Name the 6 contact forces
-friction
-applied
-compression
-normal
-air/ water resistance
-tension
Name the 3 non contact forces
-electrical
-weight
-magnetic
Name 2 types of friction
-static
-dynamic
define friction
force that opposes one surface moving or tying to move past another (opposes motion)
define static friction
force that keeps object at rest
define dynamic friction
opposes sliding or rolling motion
When walking on the floor what forces magnitude are equal or not equal to each other
-normal = weight
-thrust is more than resisting force (friction and air resistance combined) because the person is able to moving
Why do we not sink into the floor or float
because normal force is equal to weight
Which is bigger: static or dynamic friction
static friction
Which friction is on a object at rest
static
what is resisting force
force opposing another force
What is resultant force
a single force that can replace all individual forces acting on the object, and have the same effect
How do you find the resultant force
-arrows in same direction = add the forces
-arrows in different direction = minus the forces and the greater force will the the resultant force in the greater force direction
-if minus becomes 0, the resultant force is 0 so stationary
Which directions can a force move in
North, South, East, West and anywhere in between
What are the effects of friction
opposes motion, creates heat
What is the unit for force
Newtons (N)
define Newton’s 1 law
An object will remain stationery ( at rest) or move in a constant (uniform) speed in a straight line unless a net resultant force acts on it
define Inertia
an objects resistance to change in speed and its direction
What is the relationship between Mass and Inertia
As mass increase, Inertia increases
What is the effect of increased Inertia
greater Inertia, more difficult to move the object when stationary or change its speed or direction when moving
What is the mass of a body
measure of Inertia
State Newton’s 3 law
for every action, there is an equal and opposite force on it (forces act in pairs)
Define balanced
forces in opposite directions that have the same magnitude
how does forces always act in
pairs
What does every object with a mass have
a gravitational field
an object with a constant speed has what forces that are?
forward and backward forces that are balanced
When will there be in unbalanced forces
acceleration
define Newton’s 2 law - symbols and words
force = mass x acceleration
F = ma
What are the units in Newton’s second law
-Force - Newtons (N)
-Mass - Kilograms (Kg)
-Acceleration - ms^-2
What is the relationship between force and acceleration
as forces increases, acceleration increases
mass is constant
What is the relationship between Mass and acceleration
as mass increases, acceleration decreases
force is constant
Write down the symbols and units for:
-weight
-force
-mass
-velocity
-speed
-acceleration
-weight - w, N
-force - F, N
-mass - m, kg
-velocity - v, ms^-1
-speed- s, ms^-1
-acceleration - a, ms^-2
define human reaction time
time taken for a human reaction
When happens when:
-a force is applied to a spring
-the forces is removed from the spring
- keep applying a force on the spring
-stretch the spring too far
- change shape
-return to original shape
-keep getting bigger
-spring expands to a point where it cannot return back to its original shape
what are the 2 purposes for springs
tension, compression
define elastic object
an object that returns back to its original shape
When drawing graph, where must the line of best fit start from
the origin
give 3 examples of elastic objects
rubber band, spring , sponge
Define limit of proportionality
-the point beyond which the extension of an elastic object is no longer directly proportional to the force applied to it
-(where it stop being proportional)
What is Hooke’s law
the extension of a spring is directly proportional to the force applied to it until it exceeds the limit of proportionality
define spring constant measure
stiffness of the spring
what is the relationship between the spring constant and the stiffness of the spring
as spring constant increases, stiffness of the spring increases
What is the formula for spring extension - symbols and words
Force = spring constant x extension of spring
F = kx
What are the units in the formula for spring extension
-Applied Force = Newtons (N)
-Spring constant = Newtons per meter (Nm^-1)
-extension = meters (m)
How do you find the extension of a spring
stretched length - original length
Give 2 places tension springs are used
machines and trampolines
(creates suspension)
Give 2 places compression springs are used
pens, cell phones
define moment
turning force
which 2 direction can a moment turn into
clockwise, anti-clockwise
Explain the resultant force in a moment
difference between clockwise and anti-clockwise moments, needs to have a magnitude and direction (unbalanced)
define Equilibrium in a moment
the clockwise and anti-clockwise moments are equal (balanced) = resultant force and resultant moment are 0
define pivot
turning point (needs to touch the surface)
where is the force applied and which direction on a beam with pivot
at the end of the beam, down
How are the arrows in a moment drawn
draw the arrow as the size of the force and the direction of the force (curved)
What is the formula for moment - symbols and words
moment = force x perpendicular distance from the pivot
m = Fd
What are the units for the formula for moment
-moment - Newtons x meters (Nm)
-Force - Newtons (N)
-distance - Meters (m)
Define distance in moment
distance has to be perpendicular to pivot from the force
Define center of gravity
point where whole weight of object seems to act
what is the requirement for a regular shape
needs at least 1 line of symmetry
define a regular shape
has 1 or more lines of symmetry
How do you find centre of gravity for regular shapes
do lines of symmetry and the middle where the lines intersect is the center of gravity
What must you do when you draw the lines of symmetry and find the centre of gravity
label them
How do you find center of gravity for irregular shapes
-on a retort stand place the cork
-poke a hold into the shape and place it hanging freely using a nail
-place a bob on the cork and draw a line on following the string of the bob on the shape. Repeat 3 time, each time poking holes in different places
How is an object stable
the center of gravity is within the base of the object
define stability
how likely an object will fall when disturbed
relationship between the base and stability
-bigger the base, more stability
relationship btw center of gravity and stability
-higher center of gravity, less stability
Name 3 types of equilibrium and explain them
-stable equilibrium - object returns to its original equilibrium position
-unstable equilibrium- object does not return to its original equilibrium position
-Neutral equilibrium - object remains in displaced position
what is the difference between w = fd and m = fd
w = fd - d- distance + displacement
m = fd - d - physical distance
what are equal when balanced (moment)
anti - clockwise moment = clockwise moment
what is pressure
force per unit area
what is the equation for pressure in solid
p = F / A
pressure = force / area
what is the units for pressure in solids
p= Pa (pascal) / Nm ^-2 / Ncm ^-2
F= N
A = m^2
note: 10000cm ^2 = 1m ^2
Note: be careful with the unit for area
as area increases, pressure?
decreases
as force increased, pressue?
increases
what is the equation for pressure in liquids
p = hpg
pressure = height x density x gravity
what is the units for pressure in liquids
p = Pa
h = m
p = density
g =NKg ^-1 (9.8)
how does pressure act at 1 depth in liquids
equally in all directions
what does pressure not depend on
size and shape of the container
