Studied by 2 people
Properties of weight
Force must act on the centre of mass of an object
Caused by the Earth’s gravity
Always drawn down
Properties of tension
Pulling/pushing force acting on a taut string
Pulling/pushing force acting on a deformed spring
Acts on either end of the string/spring
The pair of forces are always equal in magnitude
Properties of the normal force/reaction force
Force acting on an object from the surface it is in contact with
Reaction to force acting on the surface by the object
Force vanishes when the contact is lost
Always perpendicular to the surface
Properties of friction
Force opposing the relative motion between two surfaces
The sum of many tiny forces that emerge from the irregularity of the two surfaces
Acts parallel to the surface
Properties of lift
The force that keeps flying objects in the air
Direction (acting?) is upwards
Properties of upthrust
The force acting on an object that has been partially or wholly submerged in a liquid
Direction (acting?) is upwards
Properties of drag
The force opposing the motion of an object inside a fluid (air/water)
Acts opposite to the direction of velocity
Air resistance for air
Vanishes in a vacuum
Often ignored as it can often be very small
Properties of the resultant force
The sum of all the forces acting on an object
Not an actual force, it’s the result of a calculation
Each object has its own resultant force
Can be equal to a single force (e.g. only one force acting on an object)
What is a vector?
An object that has both direction and magnitude. All forces are vectors.
What does an object being in equilibrium mean?
When the resultant force of an object is equal to zero. If all the forces acting on an object cancel out. Described by Newton’s first law of motion
What is Newton’s first law of motion?
If an object is at rest, it remains at rest. If an object is in motion, it remains at a constant velocity. Unless another force acts on the object.
What does it mean when the forces are balanced/object is in balance?
An object is at equilibrium - resultant force = 0
What does it mean when an object is unbalanced?
The resultant force acting on an object does not equal zero. Described by Newton’s second law.
What is Newton’s second law of motion?
F = ma, the acceleration of an object depends on:
Resultant (net) force
mass of the object
What is a free-body diagram?
A diagram of an object which details all the forces acting on an object, and excludes all other forces.
What is the symbol and equation for weight?
W = m x g (where g is gravitational field strength)
What is the symbol and equation for tension?
T = mg + ma
What is the symbol and equation for the normal force?
N (no equation)
What is the symbol and equation for friction?
F (equation only used in mathematics, not physics)
What is the symbol and equation for lift?
sometimes L (no equation)
What is the symbol and equation for upthrust?
sometimes U (no equation)
What is the symbol and equation for drag?
n/a
What is the symbol and equation for resultant force?
F (equation specific to scenario)
Compression
Opposite of tension
(do I need to know this)
When can Newton’s second law be applied?
F = ma only applied when the mass is constant
What is terminal velocity?
The maximum velocity an object can reach when falling (with air resistance)
Explain how an object reaches its terminal velocity.
Object initially freefalls, therefore acceleration is due to gravity, and its weight is the only force acting on it
As object accelerates, the drag force on the object also increases (increase in velocity causes increase in drag)
This decreases the resultant force on the object
F = ma, therefore the acceleration also decreases
When the drag force = weight of object, the resultant force and acceleration is 0
The object has reached its terminal velocity.
Note 
Flashcard (63)