Separate Physics - 6.5 Flashcards
What are physical quantities with only magnitude (and no direction)?
Scalar quantities
What are physical quantities with magnitude and direction?
Vector quantities
Give some examples of scalar quantities
- Speed
- Distance
- Mass
- Temperature
- Time
Give some examples of vector quantities
- Force
- Velocity
- Displacement
- Acceleration
- Momentum
What does the arrow for a vector quantity show?
The length of the arrow shows the magnitude and the direction of the arrow shows the direction of the vector quantity
What is a force?
A push or pull acting on an object due to the interaction with another object
What are forces between objects classified as?
Contact or non-contact forces
Describe contact forces
Forces between objects that are physically touching
Describe non-contact forces
Forces between objects that are physically separated
Give some examples of contact forces
- Friction
- Air resistance
- Tension
- Normal contact force
Give some examples of non-contact forces
- Gravitational force
- Electrostatic force
- Magnetic force
What type of quantity is force?
A vector quantity
What is weight?
The force acting on an object due to gravity
What cause the force of gravity close to the Earth?
The gravitational field around the Earth
If mass it constant, what can affect the weight of an object?
The gravitational field strength at the point where the object is
How can the weight of an object be calculated?
What are the units for gravitational field strength?
Gravitational field strength, g, measured in N/kg
What is an object’s centre of mass?
The weight of an object acting at a single point
What does W ∝ m mean?
The weight and mass of an object are directly proportional
How is weight measured?
A calibrated spring-balance (newton meter)
What is a ‘resultant force’?
A single force, replacing a number of forces, acting upon an object
What has happened if a resultant force moves an object?
Work is done
What is the equation for work done?
When a force causes an object to move through a distance what has happened?
Work is done on the object so a force does work on an object when the force causes a displacement of the object
What is one joule of work done?
When a force of one newton causes a displacement of one metre
What does 1 joule equal?
1 newton-metre
What happens to temperature when work done occurs against frictional forces on an object?
Temperature increases
How many forces need to change the shape of an object (by bending, stretching or compressing)?
More than one
What has happened if an object has been inelastically deformed?
It doesn’t return to its original shape and length after a force has been removed
What has happened if an object has been elastically deformed?
It returns to its original shape and length after a force has been removed
What has happened if an object has been elastically deformed?
The extension of an elastic object is directly proportional to the force applied
What is the equation that links force, spring constant and extension?
When a spring is compressed what does the ‘e’ in ‘F = k e’ represent?
‘e’ would be the compression of the object (the difference between the natural and compressed lengths)
Why type of energy is stored when a force does work on a spring?
Elastic potential energy
Separate Q. What may cause an object to rotate?
A force or a system of forces
Separate Q. What is a moment?
A turning effect of a force
Separate Q. How can the size of a moment be calculated?
Separate Q. What moments are experienced by a balanced object?
The total clockwise and total anticlockwise moments about the pivot are equal
Separate Q. What can be used to transmit rotational effects of forces?
Simple levers and simple gear systems
Separate Q. What is a fluid?
A liquid or a gas
Separate Q. How can pressure in fluids be described?
The pressure causes a force normal (at right angles) to any surface
Separate Q. How can the pressure at the surface of a fluid be calculated?
Separate Higher Q. What happens to atmospheric pressure as height is increased?
It increases
Separate Higher Q. What does pressure in a liquid depend on?
The depth and the density
Separate Higher Q. If an object floats, what is the relationship between its weight and upthrust?
Weight = upthrust
Separate Higher Q. For a submerged object (partially or totally) where is the pressure greatest and what does this cause?
Pressure is greatest at the bottom creating a resultant force upwards (upthrust)
Separate Higher Q. What happens to an object if it is denser than the fluid it is placed in?
It will sink – it weighs more than the equivalent volume of fluid it has displaced
Separate Higher Q. What happens to an object if it is less dense than the fluid it is placed in?
It will float – it weighs less than the equivalent volume of fluid it has displaced
Separate Q. What is the atmosphere around Earth and how does it change with altitude?
A thin layer of air around the Earth which gets less dense with increasing altitude
Separate Q. What causes atmospheric pressure?
Air molecules colliding with a surface
Separate Q. Why does atmospheric pressure decreases with increasing altitude?
The number of air molecules (and therefore the weight) decreases with an increase in height
What is distance?
How far an object moves (a scalar quantity) which does not involve direction
What is displacement?
Displacement includes both the distance an object moves and the direction (a vector quantity)
What does speed not involve?
Direction (it is a scalar quantity)
What are typical speed values for someone walking, running and cycling (m/s)?
- Walking 1.5 m/s
- Running 3 m/s
- Cycling 6 m/s
Is the speed of sound (and that of the wind) constant?
No – the speed of sound (and that of the wind) can vary
What is the typical value for the speed of sound (m/s)?
330 m/s
How can distance travelled be calculated?
What is the velocity of an object?
Velocity is speed, in a given direction (a vector quantity)
Higher Q. How can the motion of an object in a circle be described?
Constant speed but changing velocity
If an object is moving in a straight line how can the distance travelled be represented?
Distance-time graph
How can the speed of an object be calculated in a distance-time graph?
The gradient
Annotate the following distance-time graph:
Higher Q. For an accelerating object, how can the speed at a given point be determined?
A tangent can be drawn measuring the gradient of the distance-time graph at that specific time
How can acceleration be calculated?
What is happening to an object which is slowing down?
It is decelerating
Draw a velocity-time graph for two vehicles – one with a constant acceleration and one with a constant acceleration, a constant velocity and a constant deceleration
Higher Q. How can the displacement of an object (the distance travelled) be calculated from a velocity-time graph?
The area under a velocity-time graph
What is the acceleration of any free-falling object near the Earth’s surface?
9.8 m/s2
What initially causes an object falling through a fluid to accelerate?
The force of gravity
Why does an object reach terminal velocity?
The resultant force becomes zero
What does Newton’s First Law state (for a stationary object)?
If the resultant force is zero a stationary object remains stationary
What does Newton’s First Law state (for a moving object)?
If the resultant force is zero a moving object continues to move at the same velocity
How can the forces be described for a vehicle moving at a steady speed?
The resistive forces balance the driving force
What causes the velocity of an object to change?
The resultant force acting on the object must change
Higher Q. What is inertia?
The tendency of objects to continue in their state of rest / uniform motion
What is Newton’s Second Law?
The acceleration of an object is proportional to the resultant force acting on the object (and inversely proportional to the mass of the object)
What is the equation for Newton’s Second Law?
Higher Q. What is inertial mass?
A measure of how difficult it is to change the velocity of an object
Higher Q. How can inertial mass ratio be defined?
The ratio of force over acceleration
What are typical everyday speeds for cars, trains and planes?
- Car 25 m/s
- Train 55 m/s
- Plane 250 m/s
What is Newton’s Third Law?
Whenever two objects interact, the forces they exert on each other are equal and opposite
How can the stopping distance of a vehicle be calculated?
The sum of the thinking distance and the braking distance
What is thinking distance?
The distance covered during the driver’s reaction time
What is braking distance?
The distance covered during the braking force
For a given braking force, what does greater speed cause?
A greater stopping distance
What are ‘typical’ reaction times?
0.2 s to 0.9 s
What can affect a driver’s reaction time?
- Tiredness
- Drugs
- Alcohol
What can affect the braking distance of a vehicle?
- Road conditions
- Weather conditions (wet / ice)
- Vehicle conditions (brake / tyre quality etc…)
What happens when a force is applied to the brakes of a vehicle (in terms of energy)?
Work done by the friction force between the brakes and wheel reduces kinetic energy of the vehicle (and brake temperature increases)
How does increases the speed of a vehicle affect the braking force?
A greater braking force is needed to stop the vehicle in a given distance
What does a greater braking force allow?
A greater deceleration
What can large decelerations lead to?
Brakes overheating / loss of control
How is momentum calculated?
What is the conservation of momentum?
In a closed system, the total momentum before an event is equal to the total after an event
Separate Q. What happens to momentum when a force acts on a object that is moving or able to move?
A change in momentum occurs
Separate Q. What safety features are present to reduce momentum changes?
Air bags, seat belts, crash mats, cycle helmets, cushioned surfaces etc… All aiming to reduce momentum change
