P1- motion, forces, energy (forces, moment, pressure) Flashcards
Define force
-push, pull or twist
-causes change in speed, direction, shape
-measured in Newtons
Which type of quantity are forces
-vector, so needs arrow heads
-arrow size - magnitude of force
-arrow head - direction of force
-Always label your arrows magnitude
name the 9 types of forces
-first 6 are contact force
-last 3 are non- contact forces
-friction
-applied
-compression
-normal (upthrust, buoyancy for in water)
-air/ water resistance
-tension
-electrical
-weight
-magnetic
Name the 6 contact forces
-friction
-applied
-compression
-normal
-air/ water resistance
-tension
Name the 3 non contact forces
-electrical
-weight
-magnetic
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 move
Why do we not sink into the floor or float
because normal force is equal to weight
define friction
force that opposes one surface moving or tying to move past another (opposes motion)
Name 2 types of friction
-static
-dynamic
define static friction
force that keeps object at rest
define dynamic friction
opposes sliding or rolling motion
Which is bigger: static or dynamic friction
static friction
Which friction is on a object at rest
static
What are the effects of friction
-opposes motion
-creates heat
what is resisting force
force opposing another force
What is resultant force
a single force that replaces 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
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, harder 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 always act in pairs
Define balanced
forces in opposite directions with the same magnitude
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
-Newtons
-as forces increases, acceleration increases; mass is constant
-as mass increases, acceleration decreases; force is constant
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 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 the formula for spring extension - symbols and words
Force = spring constant x extension of spring
F = kx
-Applied Force = Newtons (N)
-Spring constant = Newtons per meter (Nm^-1)
-extension = meters (m)
what is the relationship between the spring constant and the stiffness of the spring
as spring constant increases, stiffness of the spring increases
formula for extension of a spring
stretched length - original length
define spring constant measure
stiffness of the spring
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 & examples
-an object that returns back to its original shape
-rubber band, spring , sponge
Give 2 places tension & compression springs are used
-first 2 are tension
-last 2 are compression
-machines
-trampolines
-pens
-cell phones
Principle of moment
anti clockwise moment = clockwise moment
define moment
turning force
which 2 direction can a moment turn to
-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)
Define distance in moment
distance has to be perpendicular to pivot from the force
formula for moment - symbols and words
moment = force x perpendicular distance from the pivot
m = Fd
-Nm (Newton x meters)
Define center of gravity
point where whole weight of object seems to act
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
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 pressure
force per unit area
what is the equation for pressure in solid
p = F / A
pressure = force / area
- Pa (pascal) / Nm ^-2
F= N
A = m^2
-10000cm ^2 = 1m ^2
what is the equation for pressure in liquids
p = pgh
pressure = density x gravity height
how does pressure act in liquids
equally in all directions
what does pressure not depend on
size and shape of the container
