Flashcards in Forces Deck (42):
What is a vector?
Has magnitude and direction.
What is a scalar?
A physical quantity that has magnitude.
Examples of scalars
Examples of vectors
What do forces make an object do?
What are the contact forces?
What are the none contact forces?
What is weight?
The weight of an object is the force acting on it due to gravity. Weight is measured in Newtons (N).
What is mass?
The mass of an object depends on the quantity of matter in it. Mass is measured in kilograms (Kg).
What is the equation for weight?
Weight = mass x gravitational field strength
W= m x g
What is terminal velocity?
Terminal velocity is when the object reaches a constant velocity when the frictional force in it is equal and opposite to its weight. The resultant force is then 0 so the acceleration is 0.
What is the resultant force of an object released in fluid?
The weight - frictional force
What is the centre of mass of an object?
The centre of mass of an object is the point at which it’s mass can be thought of as being concentrated.
What two factors affect the stability of an object?
The width of the base of an object
The height of its centre of mass- higher centre of mass = less stable
How do you work out the centre of mass of an irregular shape?
Cut out irregular shape
Put hole in corner
Use clamp stand to suspend it and draw vertical line using plumb line
Repeat hanging the shape from different corners
Where all lines meet is the centre of mass.
What are forces in an interaction pair?
They are equal in size and opposite in direction.
What is the resultant force when an object is balanced?
Resultant force= 0
What happens when forces are imbalanced?
The object can change speed direction or shape.
What is work done?
Work is the amount of energy transferred to move a certain distance
What is the equation for work done?
Work done= force x distance
What is Hooke’s law?
The extension of a spring is directly proportional to the force applied as long as the limit of proportionality isn’t exceeded.
What is the equation for force applied?
Force applied= spring constant x extension
F= k x e
Parallelogram of forces
Need a scale
Draw parallelogram using angles and lengths (see book)
Find the length of the dotted line
Person walking: 1.5
Person cycling: 6
Person running: 3
Wind on windy day: 18
Car in motorway: 31
Car in built up area: 13
Sound in air:330
* all in m/s
Speeds are rarely constant, called ununiform
What is speed?
Speed is a scalar. It is how fast you are travelling
What is velocity?
Velocity is a vector. It is speed in a given direction
What is acceleration?
Acceleration is the change in speed or velocity over time. If negative it is called deceleration.
What is the equation for acceleration?
A= change in velocity/ time taken
How do you find distance on a velocity time graph?
Area under the graph
What is the equation for a constantly accelerating body?
V^2 = u^2 + 2as
Final velocity = initial velocity + (2 x acceleration x displacement)
What is Newton’s 1st law?
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted on by an imbalanced force
The tendency of an object to stay at rest or move in uniform motion is called inertia. The inertia of an object depends on its mass.
What is Newton’s 2nd law?
The acceleration of an object is proportional to the resultant force of an object and inversely proportional to the mass of an object.
What is Newton’s 3rd law?
For every action there is an equal and opposite action. Forces which are in equilibrium are equal and opposite.
What is the equation for force?
Force = mass x acceleration
Factors effecting top speed
Surface of road
Air resistance/ aerodynamics/ stream lining
Power of engine
How do you find stopping distance?
Stopping distance= thinking distance + braking distance
Factors effecting thinking distance
Distractions (people phone music)
Factors effecting braking distance
Surface of road
Quality of brakes
Quality of tyres
Weight of car
Speed of car
Gradient of the road
What is the equation for momentum?
Momentum= mass x velocity
Momentum is measured in kg m/s
What is momentum affected by?
Mass: larger mass= larger momentum
Velocity: the faster the object moves the larger the momentum
What happens to momentum when no external forces act?
Momentum is conserved
Momentum before= momentum after