- Created by: CPev3
- Created on: 04-05-20 23:54
What is a couple?
A pair of equal and opposite forces acting on a body but not in the same straight line
What is the torque of a couple?
The product of one of the forces of a couple and the perpendicular distance between the forces
Torque = F * d
What is a torque?
The moment of a couple
What are the rules of the triangle of forces?
- The resultant of forces F and T must be equal in magnitude to the third force W but in the opposite direction
- Both the resultant vertical force and resultant horizontal force must be zero
What is a triangle of forces?
- Arrows are drawn to represent each of the 3 forces end-to-end
- The triangle is closed because the net force is zero and so the object is in equilibrium
What is density?
The mass per unit volume of a substance
ρ = m / V
What is the density of air?
What is pressure?
The normal force exerted per unit cross-sectional area
p = F / A
What is the value of atmospheric pressure?
What is weight?
The gravitational force acting on an object through its centre of mass
What is friction?
The force that arises when two surfaces rub against each other
What is drag?
The resistive force on an object travelling through a fluid
What is tension?
The force within a stretched cable or robe
What is upthrust?
An upward buoyancy force acting on an object when it is in a fluid
What is normal contact force?
A force arising when one object rests against another object
Weight resolved into two components:
Force parallel to the slope = mgsinθ Force perpendicular to the slope = mgcosθ
Net force equations:
Net force = m * a
Net force = normal contact force - weight
What factors affect the magnitude of drag?
- Cross-sectional area
- Roughness/ texture of object
- Density of fluid
How can you reduce the air resistance exerted agai
Smooth, streamlined shape
Increases the top speed of the car
Reduces the amount of fuel used on a journey
What is terminal velocity?
The constant speed reached by an object when the drag force (and upthrust) is equal and opposite to the weight of the object
What is a moment?
The product of force and perpendicular distance of the line of action of force from the axis or point of rotation
Moment = F * x
What is the moment of a force?
The turning effect of a force about some axis or point
The principle of moments:
When a body is in equilibrium, both the net force and net moment acting on it is zero
The sum of the anticlockwise moments about any point = the sum of the clockwise moments about that same point
Stages of terminal velocity:
t = 0
net force = mg
a = g
mg > D
net force = mg - D
a = (mg - D) / m
mg = D
net force = 0
a = 0
What is centre of gravity?
An imaginary point at which the entire weight of an object appears to act
What is centre of mass?
A point through which any externally applied force produces straight-line motion but no rotation
How do you fing the centre of gravity of an object
1) Make small holes along the edges of the object made from card
2) Insert a pin through one of the holes and hold the pin firmly in a clamp
3) Allow the object to swing freely before coming to rest with its CoG vertically below the pin
4) Hang a plumb-line from the pin
5) Draw a line along the vertical string of the plumb line
6) Repeat this process for the other holes
7) CoG = the point of intersection of the lines
What is a fluid?
A substance that can flow
The pressure exerted by a vertical column of liqui
W = m * g
W = (ρ * V) * g
W = ρ * A * h * g
p = (ρ * A * h * g) / A
p = h * ρ * g
- The upthrust exerted on a body immersed in a fluid (fully/ partially submerged) = the weight of the fluid that the body displaces
- An object will sink if the upthrust is less than the weight of the object
- For a floating object the upthrust = the weight of the object = the weight of the fluid it displaces
Force at the top surface = h ρ * g * A
Force at the bottom surface = (h + x) * p * g * A
Resultant upward force (upthrust) = ((h + x) * p * g * A) - (h * ρ * g * A) = x * ρ g * A