Forces In Action Flashcards
What is the force, mass & acceleration equation?
F = ma
F = force, N
m = mass, kg
a = acceleration, ms^-2
What is one Newton?
The force that will give a mass of 1kg an acceleration of 1 ms^-2
What is the SI base unit for the Newton?
Kg ms^-2
What is the weight, mass and acceleration of free fall?
W = mg
W = weight, N
m = mass, kg
g = acceleration of free fall, ms^-2
What is acceleration of free fall on earth?
9.81
When is an object in free fall?
When it is falling solely under the influence of gravity
What is the tension?
The force experienced by a cable, role or string when pulled, hung, rotated or supported
What is the normal contact force?
The force arising when when an object rests against another object at a 90 degree angle to the plane of contact
What is upthrust?
The upward force acting on an object when it is in a fluid
What is friction?
The force that arises when 2 surfaces are in contact with one another
What are free-body diagrams used for?
Modelling the forces that are acting on an object
What do arrows represent on a free body diagram?
Each force, where each arrow:
- Is scaled to the magnitude of the force it represents
- Points in the direction that the force acts
- Is labelled with the name of the acting force
What is the component of the force that acts perpendicular to the slope on an object?
W cos θ
What is the component of the force that acts parallel to the slope on an object?
W sin θ
What are drag forces?
Forces that oppose the motion of an object moving through a fluid (gas or liquid)
What are the features of drag forces?
- Are always in the opposite direction to the motion of the object
- Never speed an object up or start them moving
- Slows down an object or keeps them moving at a constant speed
- Covert kinetic energy into heat and sound
Whats the relation between driving force and frictional force when an object is accelerating?
Driving force > frictional force
Whats the relation between driving force and frictional force when an object has constant velocity?
Driving force = frictional force
Whats the relation between driving force and frictional force when an object is decelerating?
Driving force < frictional force
What does the magnitude of the drag force depend on?
- The speed of the object
- The objects shape and texture
- The density of the fluid
What are the 2 most significant factors that effect the magnitude of the drag force?
- Speed of the object
- Cross-sectional area
When does air resistance increase?
When the speed of an object increases
What factors can affect the maximum speed of an object?
- Cross-sectional area
- Shape
- Altitude
- Temperature
- Humidity
Why are experimental values of the acceleration of free fall usually less than 9.81 ms^-2?
Because there are drag forces acting against the motion of the object which decrease the net force, therefore decreasing the acceleration
What is terminal velocity?
When the drag force is equal to the gravitational pull (weight) on the body, the body will no longer accelerate and will fall at a constant velocity
What does a terminal velocity graph look like?
How do you investigate terminal velocity?
What is a moment?
The turning effect of a force - they occur when forces cause objects to rotate about some pivot
What is the equation for a moment?
Moment (Nm) = force (N) x perpendicular distance from pivot (m)
What is a couple?
A pair of equal and opposite coplanar forces that act to produce rotation only
What are the factors of the pair of forces in a couple?
- Equal in magnitude
- Opposite in direction
- Perpendicular to the distance between them
What is the resultant force of the couple?
0 N
What is torque?
The moment of the couple
What is the equation for torque?
Torque = force (of one force) x perpendicular between the forces
What is the principle of moments?
For a system to be in equilibrium, the sum of clockwise moments about a point must be equal to the sum of the anticlockwise moments about the same point
What is centre of mass?
The point at which the weight of an object may be considered to act
In a uniform gravitational field, where is the centre of gravity?
Where the centre of mass is
What does the centre of gravity depend on?
The gravitational field
How do you find the centre of mass?
1) Hang up the irregularly shaped object
2) Suspend the shape from a location near an edge. Drop a plumb line and mark on the object
3) Suspend the shape from another location (not too close to the first) and drop the plumb line again and mark its position
4) Where the 2 lines cross is the centre of mass
When is a system in equilibrium?
When all forces are balanced:
- There is no resultant force
- There is no resultant torque
When are forces in equilibrium?
When an object is at rest or moving with constant velocity
What is density?
mass per unit volume of an object
What is the density equation?
ρ = m/ v
ρ = density (kg m^-3)
m = mass (kg)
v = volume (m^3)
What is the volume of a sphere?
4/3 πr^3
What is the volume of a cube?
d^3
What is the volume of a cylinder?
pi r^2 l
What is pressure?
Force per unit area
What is the equation for pressure?
P = F/ A
P = pressure, Pa
F = force, N
A = area, m^2
What is the equation containing both pressure and density?
P = ρgΔh
P = change in pressure, Pa
Δh = change in height, m
g = acceleration due to gravity
ρ = density, kg m^-3
What is Archimedes principle?
An object submerged in a fluid at rest has an upward buoyancy force - upthrust - equal to the weight of the fluid displaced by the object
What is the upthrust equation?
F = ρgV
F = upthrust, N
ρ = density of fluid, kg m^-3
g = acceleration due to gravity
V = volume dispalced
