P2- Forces Flashcards
What does a vector quantity have?
Direction and magnitude
What quantity is force?
Vector
Give 5 examples of a vector quantity
Force, velocity, displacement, acceleration, momentum
What does a scalar quantity have?
Magnitude and no direction
Give 5 examples of a scalar quantity
Speed, distance, mass, temperature, time
What are vectors usually represented by in diagrams?
Arrows
What do the length and direction of a vector arrow show?
Length shows the magnitude and the direction shows the direction of the quantity
What is gravitational force?
The force of attraction between masses
What is mass?
The amount of matter in an object
What is weight?
The amount of gravitational force acting on an object
What is the difference between mass and weight?
Mass will always stay the same and weight would change in different parts of the universe
What is weight measured in and how?
Newtons with a calibrated spring balance or newtonmeter
What is mass measured in?
Kilograms
How can you calculate weight using mass?
Weight = Mass X Gravitational Field Strength
What happens when a force moves an object through a distance?
Energy is transferred and work is done
What is work done?
The amount of energy transferred to an object by an external force when it is moved over a certain distance by that force
What does it mean if an object is in equilibrium?
The forces acting on it are balanced
What is the phrase used when a spring is stretched so far it cannot return to its original form?
Limit of proportionality
What is extension directly proportional to?
Force
When does extension stop being directly proportional to force?
When the force is too great and the spring reaches its limit of proportionality
What is a moment?
A force can cause an object to rotate, the turning effect of a force is its moment
What is the equation linking moments to force?
Moment = Force x Distance
How do levers make it easier to do work?
They increase the distance from the pivot at which the force is applied and since M=FD, less force is needed to get the same moment
How do gears work?
They transmit rotational effects, their teeth interlock causing a domino effect of turning, the larger gear will turn slower than the smaller gear
What is pressure?
The force per unit area
How does density affect the pressure in a liquid?
The denser the liquid is, the more particles there are, which means more particles collide and therefore increase the pressure
How does depth affect the pressure in a liquid?
As the depth of a liquid increases, the number of particles above that point increases, the weight of these adds to the pressure felt at that point
What do objects in fluid experience?
Upthrust
What is upthrust?
A resultant force upwards that is equal to the weight of fluid that has been displaced by the object
Why do objects float or sink in water?
If the objects weight is equal to the upthrust it will float as the forces balance, but if the object is more or less dense than the forces are unequal and the less dense object will displace water and sink, and the more dense object will sink immediately
What is atmospheric pressure?
Created on a surface by air molecules colliding with the surface
When does atmospheric pressure increase and decrease?
When altitude increases it decreases as the atmosphere gets less dense so there are fewer air molecules to collide with
What is the difference between speed and velocity?
Speed is how fast you are going, and is scalar, velocity is the speed in a given direction and is a vector
What is the similarity between speed and velocity?
They both measure how fast something is going
What is acceleration?
The change in velocity in a certain amount of time or how quickly something speeds up
What is deceleration?
The speed in which something slows down or negative change in velocity
What is another word for constant acceleration?
Uniform acceleration
What is an example of uniform acceleration?
Acceleration due to gravity for objects in free fall
When does friction occur?
Between two surfaces in contact, the friction is the opposite direction to the movement, or when an object passes through a liquid (this is called drag)
When does drag increase?
When speed increases
What do objects falling through fluid eventually reach?
A terminal velocity
How do objects reach terminal velocity?
At first gravity is stronger than friction, as speed increases so does friction, this reduced acceleration till it is equal to friction (resultant force is zero), it will have reached maximum speed or terminal velocity
What happens at terminal velocity?
The object will fall at a steady speed
What is Newtons first law of motion?
Every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. A force is needed to change motion.
When did Isaac Newton create the laws of motion?
1660s
What is Newtons second law of motion?
The time rate of change of the momentum of a body, is equal in both magnitude and direction to the force imposed on it. Acceleration is proportional to the resultant force.
What is inertia?
The tendency for motion to remain unchanged. The tendency that until acted upon by a resultant force, objects stay at rest or stay moving.
What does an objects inertial mass measure?
How difficult it is to change the velocity of an object
How can inertial mass be found?
Newtons second law which states F=ma or Resultant force = acceleration x mass
What is Newtons third law?
To every action, there is always opposed an equal reaction. Equal and opposite forces act on interacting objects.
What is a stopping distance?
The shortest possible distance it takes to stop something using maximum force
What is stopping distance equal to?
Thinking distance + braking distance
What is thinking distance?
How far the object travels during reaction time
What is braking distance?
The distance taken to stop under braking force
What affects thinking distance?
Alcohol, caffeine, fatigue, distractions, speed and reaction time
What affects braking distance?
Poor brake and tyre conditions, road surface, weather and vehicle speed
How do brakes work?
They cause friction between the brakes and the wheels
How can you measure reaction time?
By using the ruler drop test, hold a ruler between someone’s thumb and forefinger, drop it without warning, measure where they catch it and use that and the constant acceleration due to gravity, about 9.8m/s to calculate how long it falls for.
What is equal to momentum?
Mass x velocity
What does conservation of momentum mean?
In a closed system the total momentum before an event is the same as after the event
