Module 3 - Chapter 4 - Forces in action Flashcards
What is the equation for force?
F = ma
Force = mass x acceleration
What is the unit for force?
Newtons (N)
What is the equation for weight?
w = mg
weight = mass x gravitational field strength
What is the unit for weight?
Newton (N)
What is the centre of gravity?
The centre of gravity is where all of an objects weight can be assumed to be acting upon
What is the difference between the centre of gravity and centre of mass?
They are normally the same but if the gravitaional field the object is in isn’t uniform, then the centre of gravity will be at a different point.
How can you find the centre of gravity?
When an object is suspended freely, its centre of gravity will naturally come to rest directly vertically below the point of suspension. Use a plumb line and a pen to mark this line. Then do it again from a different point of suspension and the point where the two lines cross is the centre of gravity.
How do you show all the forces acting on an object?
Using a free body diagram
Name 5 forces
weight
friction
drag
tension
upthrust
normal contact force
State the equations to find the force parallel and perpendicular to a slope
force parallel to the slope = wsinθ
force parallel to the slope = weight x sinθ
force perpendicular to the slope = wcosθ
force perpendicular to the slope = weight x cosθ
How would you find the normal contact force?
Using the equation to find the force perpendicular to the slope
Explain what happens when an object hits terminal velocity
When an object reaches terminal velocity, the drag force will be equal to the weight force and so there will be no vertical resultant force and the object will not be accelerating or decelerating vertically.
What is the moment of a force?
The moment of a force is the turning effect of a force about the same axis or point.
What is the equation to find the moment of a force?
moment = Fx
moment = force x perpendicular distance from the point of rotation
How would you find the perpendicular distance from a pivot if the force isn’t perpendicular?
x = (length of lever in m) x cosθ
∵ moment = F x (length of lever in m) x cosθ
State the principle of moments
The principle of moments states that: When a body is in equilibrium, the net force acting on it is zero and its net moment is zero. This means that when an object is in equilibrium, its clockwise and anticlockwise moment are equal and opposite to each other.
What is a couple?
A pair of equal and opposite forces that are parallel to each other and the same distance away from the pivot as each other. This will make the object spin without the pivot moving.
How would you find the torque?
torque of a couple = one of the forces x perpendicular separation between the 2 forces
How would you describe an object that is in equilibrium?
The object will have no resultant forces so will not accelerate in any direction.
State the equation to find density
ρ = m/V
density = mass / volume
State the equation for pressure
p = F/A
pressure = force / area
What is density?
The amount of mass per unit volume for example the amount of grams in 1m³
What is the unit for pressure?
Pa or N/m²
State the equation for pressure in a vertical column of liquid
p = hρg
pressure = height of liquid column x density of liquid x gravitational field strength
State the equation for upthrust
upthrust = Axρg
upthrust = Vρg
upthrust = volume x density of fluid x gravitational field strength
