Forces Flashcards
What is the equation for average speed?
Distance travelled/time taken
What is the equation for acceleration?
(Final velocity-initial velocity)/time taken
What is the difference between distance and displacement?
Displacement- distance in a given direction, it’s a vector (magnitude+ direction)
Distance- scalar, only magnitude
How do you determine acceleration from a velocity time graph?
The gradient
How do you determine distance travelled from the are on a velocity time graph?
Area under the line
What is the difference between speed and velocity?
Velocity is a speed in a certain direction, it’s a vector
Speed is a scalar
What is the differences between vectors and scalars?
Vectors have both magnitude and direction (velocity, force, displacement)
Scalars only have magnitude (speed, mass)
What is negative acceleration?
Deceleration
What is the equation for average velocity?
Average velocity= displacement/time
Or
(final velocity+ initial velocity)/2
What is the equation for displacement?
(final velocity + initial velocity)/2 x time
What is the equation linking final velocity, initial velocity, acceleration and displacement
V2=u2 + 2as
What are the two types of forces?
Contact and non-contact
Examples of contact forces
Friction
Air resistance
Water resistance
Tension
Driving force
Examples of non-contact forces
Weight
Gravitational force
Electrostatic force
What can forces so to an object?
Change speed
Change direction
Change shape
What is the vector nature of forces?
Forces are vector quantities, this means that when two forces act we need to take into account the direction of these forces to find the overall net force, which is the resultant force
Calculate the resultant force of 5N are acting to the right, and 2N are acting to the left
Resultant force= 3N to the right
How do you calculate a resultant force when 2 forces are acting perpendicular?
Resultant force= force one2+ force two2 all square rooted
(Pythagoras)
What is Newtons first law of motion?
An object will remain at rest or will move with constant velocity unless an external force acts on it
What does the first law of motion means for an object at rest?
book on a table
-resultant force is 0 as the gravitational force going down, is equal to the reaction force going up
What does the first law of motion means for an object moving at constant velocity?
Car driving
air resistance=driving force
resultant force=0N
Car continues to travel at constant velocity
What is friction?
It’s a force that always acts in the opposite direction to motion
What are the factors affecting friction?
- Type of surface (roughness)
- Mass/weight
What is the equation for weight?
Weight=mass x g (10 on earth)
Gravitational field strength is often considered to be the acceleration due to gravity
Acceleration=g
What is the equation for the resultant force?
F=ma
Resultant force= mass x acceleration
What is the equation for stopping distance?
Stopping distance= thinking distance + breaking distance
What are the factors affecting stopping distance?
Speed
Mass
Road conditions
Reaction time
In what direction does air resistance act and what does it depend on?
Air resistance acts in the direction opposite to the motion
Depends on:
The surface area
Speed
What is terminal velocity?
Terminal velocity is the name given to the constant speed of an object when the air resistance is balanced by another force, so the resultant force is =0N
When the air resistance acting on an object equals the weight forces, when the resultant force=0N, also means the acceleration is also 0m/s2
What is the equation for force applied?
F=ke
Force applied= spring constant x extension
N=N/cm x cm
How do you find spring constant on a force extension graph?
Gradient
What is the Hookes law?
The force was directly proportional the extension of am object
What are the conditions for obeying Hookes law?
Linear relationship
Go through the origin
What is elastic behaviour?
Materials which return to their original length when force applied is removed
What is plastic behaviour?
Materials that do no return to their original length after the force removed is applied
What is the elastic limit?
Maximum force that can be applies before a material becomes plastic
What is plastic deformation?
This is how much the object will have stretched by once the force is being removed from the object. Measured in mm, cm and m
What is Newton’s second law?
The resultant force applied to an object is proportional to the acceleration of the object
F=ma
What is Newton’s third law?
For every action there is an equal and opposite reaction force
Example of Newton’s third law
Swimmer applies a force to the right on the wall, but the reaction force is from the wall on the swimmer to the left
Where is the centre of mass located?
It’s located where the weight is said to act, if u suspend an injection from this point, the object will be in equilibrium (net force =0N) therefore the object is not accelerating and the object is not rotating (moment=0)
Centre of mass is found where the lines of symmetry cross over
When the objects are placed on a surface there position can be described as stable or unstable
Base is the surface that is in contact with the surface
Stable- long distance from the centre of mass to the edge of base
Unstable- centre of mass is not very far away from the base
When will an object become unstable?
When the “line of action”( straight vertical line down from the centre of mass) of the centre of mass passes beyond the edge of the base of an object, and the object topples
What is the equation for moment?
M=Fd
Moment= force applied x perpendicular distance
Nm= N x m
What is the principle of moments?
If a system is in equilibrium, then the sum of the clockwise moments will equal the sum of clockwise moments. We can use that to find unknown forces or distances in balances systems
What do we mean by equilibrium?
Net force =0N
Not rotating when Net moment= 0Nm
What is a uniform object?
The object in which the centre of mass will act in the middle of the object
