CH4 Flashcards
What is the equation which shows the relation between Mass, Acceleration and Force?
F = m*a
Where: force is measured in N, mass in Kg and acceleration in meters per second squared (ms)-2
A force of 1 N will give a mass of 1 Kg an acceleration of 1ms-2 in the direction of the force
What is the difference between Mass and Weight?
Mass: measured in Kg and it is constant for a specific object or particle.
Mass depends on the amount of matter it contains
Weight: Measured in N (Kg m s -2). Its magnitude is variable and depends on location.
Weight of an object on the surface of the hearth is the gravitational force acting on the object
What is the acceleration of an object in free fall? (What is the value of g)
g = 9.81 ms-2
What is the equation which shows the relation between Weight, gravitational field strength and mass?
W = m*g
What instrument can be used to calculate the weight of an object?
A Newtonmeter, which is calibrated to show the gravitational force acting on an object in N
What is the centre of mass of an object?
It is an imaginary point where the entire mass of an object appears to be concentrated.
What is the centre of gravity of an object?
It is a point where the resultant gravitational force on the object, its total weight W, is considered to act.
Are COG and COM in the same place?
On Earth they are in most cases in the same location. However, in locations with varying gravitational fields (eg near a massive planet) the might differ.
Why on Earth COG and COM are in most cases in the same location.
Because force of gravity is relatively uniform meaning it exerts the same gravitational acceleration on all parts of the object. In this consistent gravitational field, the location where all the mass can be concentrated (centre of mass) is also the point where the force of gravity effectively acts (centre of gravity
What is Weight?
It is 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 a object traveling through a fluid (eg air and water); the same as friction
What is tension?
The force within a stretched cable or rope
What is upthrust?
An upward buoyancy force acting on an object when it is in a fuild
What is normal contact force?
A force arising when one object rests against another objects. Normal means at right angle
Force on a slope
Pg 52 and 53 of book
What are the two most common factors affecting the magnitude of the drag force on an object?
- Speed of the object (for most objects drag force is directly proportional to speed)
- Cross-sectional area of the object
What is the drag force experienced by objects in air referred to?
Air resistance
What happens to the weight and drag force during an object’s vertical fall?
Its weight stays the same but the drag increases with the increase of speed
What is the the drag, total force and acceleration as soon as an object starts to fall?
Drag is zero and total force is equal to the weight. Acceleration is g.
What is the the drag, total force and acceleration as the an object falls?
Speed increases and this increases the magnitude of the drag force. The resultant force on the object decreases as the acceleration of the object becomes less than g
What is meant by terminal velocity?
In a falling object terminal velocity is when the drag force on the object is equal and opposite to its weight.
How are acceleration and speed at terminal velocity?
Acceleration is zero and speed is constant
What is meant by moment?
A moment is the turning effect of a force
What is the formula of moments?
Moment (N m) = Force (N) × perpendicular distance from the pivot (m)
What is the SI unit for the moment
Newton metres (N m)
State 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)
How is the perpendicular distance (x) from the pivot calculated?
x = distance cos Theta
