Topic 5 Flashcards
What is a vector quantity
+ examples
Has a magnitude and a direction
Force ,velocity , displacement , acceleration
What is a scalar quantity
+examples
Has only magnitude no direction
Speed ,distance, mass , temperature , time
Examples of contact forces
Friction , air resistance , tension
Examples of non contact forces
Magnetic force , gravitational force , electrostatic force
What are gravity’s important effects
Gives everything a weight
Makes things fall toward the ground
What is weight
The force acting on an object due to gravity
Measure in newtons
What is a resultant force
The overall force acting on an object
What happens when a force moves an object through a distance
Work is done and energy is transferred
How to we draw a scale diagram of forces in equilibrium
The tip of the last force you draw should end at the tail of the first force you drew begins
What does the equation force = ke also work for
Compression - the extension is the difference between the natural and compressed lengths
What is the limit of proportionality
The Max force that a spring can take before extension is no longer directly proportional to force
Investigating springs practical
- Measure natural length of spring with ruler clamped to stand - take reading at eye level (add a marker eg tape) to the bottom of the spring to make it more accurate
- Add mass to spring and allow it to come to rest
- Record the mass and the new length of the spring - record the extension (change in length)
- Repeat until you have enough measurements (6+)
- Plot on a graph - it will curve when the limit of proportionality is exceeded
What is a moment
The turning effect of a force
To get the max moment you must push at right angles
What do levers do
Increase the distance form the pivot so less force is needed to get the same moment
Examples of levers
Long stick , wheelbarrow
What are gears
Circular disks with teeth that interlock with other gears.
They are used to transmit rotational force
Larger - bigger moment, slower
Smaller - smaller moment , faster
What is upthrust
The resultant force cause by different amounts of pressure acting on different parts of a submerged object
It is equal to the weight of fluid that has been displaced by an object
When/how does an object float
When upthrust = the objects weight
Whether or not an object will float depends on density
Less dense(than fluid) - floats
More dense (than fluid)- doesn’t
What is the atmosphere
A thin layer of air that surrounds the earth (thin compared to size of earth)
What is atmospheric pressure
Created on a surface by air molecules colliding with the surface
What happened to atmospheric pressure as height increases
It decreases as the atmosphere become less dense so less air molecules can collide with surfaces
Distance vs displacement
Distance = how far an object moves
Displacement = distance and direction in a straight line from the starting point
What are the everyday speeds In m/s
Walking - 1.5
Running - 3
Cycling - 6
Car - 25
Train - 55
Plane - 250
What is acceleration
Change in velocity over a certain amount of time
What is the speed of sound and light in m/s
Sound - 330
Light - 300,000,000
What is the constant acceleration (uniform acceleration) of an object in free fall
9.8 m/s squared
What does the gradient of a velocity time graph give you
Acceleration
What does the area under a velocity time graph give you
The distance travelled
What do curves represent on a distance time graph
Acceleration and deceleration
What is friction drag and air resistance
Friction - acts in opposite direction to movement ,slows object down
Drag - friction through a fluid
Air resistance - type of drag but with air particles
Correlation between drag and speed
As speed increases drag increases
What happens to an object as it falls through a fluid
Quickly reaches a max speed (terminal velocity) due to gravity being greater than friction force
Acceleration gradually reduces and object falls at steady speed
What does terminal velocity depend on
Air resistance
What is Newton’s first law
If the resultant force on a stationary object is zero the object will remain stationary. If the resultant force on a moving object is zero it’ll just carry on moving at the same velocity
Newton’s second law
States that acceleration is directly proportional to the resultant force
Newtown third law
When two objects interact the forces they produce are equal and opposite
What is inertia
An objects tendency to continue the same state of motion when acted on by a resultant force
Inertial mass is calculated by f=ma (newtons second law)
Investigating motion practical
- tests Newton’s second law
1.set up trolley that holds a piece of card that will interrupt the signal from a light gate. The light gate will measure the velocity
- Connect the trolley to string that goes over a pulley and is connect to a hook with mass on
3.the weight of the hook will provide an acceleration force
- Mark the starting line on the table the trolley is on
- Place the trolley on the line and hold it in place - now hook masses onto the hook - let the hook hang so it is not loose and touching the table
- Release the trolley and record the acceleration measure by the light gate
- Repeat this twice to get an average acceleration
Varying mass and force - practical extension.
To investigate the effect of mass add masses to the trolley instead of the hook
To investigate the effect of force add the masses from the trolley to the hook one at a time with each repetition of the experiment
How can Newton’s second law explain the results of the varying mass and force practical
By adding masses to the trolley the mass of the whole system increases but the force status the same
By transferring masses from the trolley to the Hook the force increases but mass of the system doesn’t
What affects thinking distance
Speed , reaction time
Tiredness , drugs , alcohol, distractions.
What affects braking distance
Speed, weather , tyre conditions , how good your brakes are
Reaction time practical
- Sit with arm resting on edge of table - someone holds a ruler so it hangs between your thumb and forefinger
- Ruler drop without warning - you must catch the ruler as fast as possible
- Take a measurement at the point the ruler was caught
- Repeat with the same person and calculate mean
5 a blob of clay can be used at bottom of ruler to stop it waving
6 use the same ruler and same person dropping it
7 factors of reaction time can be measure eg playing music as a distraction
How does braking work
When the brake pedal is pushed the brake pads press onto the wheels which causes friction.
Kinetic -> thermal
What does speed affect in a car
Braking distance
What happens to momentum in a closed system
The total momentum before = total momentum after
- momentum is conserved
How calculate the velocity of forces which interact with one another
Momentum for = momentum after
As momentum = mass x velocity
If momentum large changes fast on a person what can occur
Injury
What can help reduce forces acting upon someone by momentum
Crumple zones
Seatbelt
Airbag
Helmet
Crash mat
