Forces - Y10 Flashcards
What are scalar quantities?
Only magnitude (size) only, NO DIRECTION
What are vector quantities?
Magnitude and direction
Examples of scalar quantities
- Speed
- Distance
- Mass
- Temperature
- Energy
- Time
What does the arrow mean?
Length = magnitude of vector
Direction = direction of vector
Examples of vector quantities
- Displacement
- Weight
- Force
- Velocity
- Acceleration
- Momentum
What is a force?
Push or pull on an object thats caused by it interacting with smth
Types of forces
- Contact
- Non-contact
What is a contact force? Give examples
2 objects need tp be touching for a force to act
* Friction
* Air resistance
* Normal contact force
* Tension in ropes
What is a non-contact force? Give examples
Objects don’t need to be touching for the force to act
* Magnetic force
* Gravitational force
* Electrostatic force
What is an interaction pair?
Pair of forces that are equal and opposite and act on 2 interacting objects
2 effects of gravity
- Gives everything a weight
- On Earth, it makes things fall towards the ground
What is weight?
Force acting on an object due to gravity
* Changes with its location
The force of gravity close to the Earth is due to the …
gravitational field around the Earth
What does the weight depend on?
- Strength of Gravitational field strength at the point where object is
What is the “centre of mass”
Where the mass is concentrated the most
What is weight measured by?
Calibrated spring balance or newtonmeter
Diff between mass and weight
Mass is not a force but weight is
What is mass measured by?
Mass balance
Formula for weight
W (g) = Mass (kg) X Gravitational Field Strength (N/kg)
What is the r/s between mass and weight?
Directly proportional
What is a resultant force?
Single force that has the same effect as all of the original forces acting together
What happens when a force moves an object through a distance?
Energy is transferred and work is done on the object
Work done equation
W (J) = F (N) s (m)
What is 1J in Nm?
1
What 3 things could happen if you apply force to an object?
- Stretch
- Bend
- Compress
How many forces do you need for an object to stretch, bend or compress? Why?
more than 1 so there is a balance, otherwise it would move in the direction of the applied force
Elastically deformed
Can go back to orignal shape and lendth after force has been removed
Inelastically deformed
Can’t go back to orignal shape and lendth after force has been removed
When is work done?
When a force stretched or compresses an object and casues energy to be transferre to the elastic potential energy store
What does it have to be for all its energy to be transferred to an objects EPS?
Elastically deformed
What is the r/s between extension of a stretched spring and force applied
Directly prop
Equation for force for Hookes Law
F = k (spring constant) e (extension)
How is the spring constant affected by?
Material you’re stretching
Stiffer spring = greater spring constant
Limit of proportionality
- When extension is no longer prop to force
- Point marked P
Moment
Turning effect of a force
Formula for size of the moment
M = F(Force) d (distance, perpendicular distance from pivot to line of action of force)
What does the force on the spanner cause?
Moment on the nut (pivot)
How to get the max moment?
Push at right angles to the spanner
Pushing at an angle means a small distance, so smaller moment
How can an object be balanced and not turn?
If total anticlockwise moment = total clockwise moment about a pivot
What do levers do?
- Increase distance from pivot at which force is applied
- M = Fd, means less force neede to get same moment
- Make it easier to work
What are gears?
Circulalar discs with “teeth” around their edges
How do gears work?
Their teeth interlock so that turning 1 causes another to turn in the opp direction
Which is faster, smaller or larger gear?
smaller
What are gears used for?
To transmit the rotational force from 1 place to another
Force transmitted to a larger gear means…
bigger moment, as distance to pivot is greater
Fluids
- Gases/liquids, particles able to move around
- Particles collide with each other+ surfaces
- Partcles are light but still have a mass and exert a force on object they collide
Pressure
Force is exerted normal (right angles) to any surface in contact with the fluid
Formula for pressure
F = PA
Force normal to a surface N/ area of that surface m2
Density
How close togther particles in a substabce are
What happens to the pressure as the depth of a liquid increases?
- No of particles above that point increases
- Weight of particles adds to the pressure felt att hat point
- Pressure inreases with depth
Formula for pressure
p = hρg
h = height of colum of liquid
g = gfs
rho = density of liquid
Process of upthrust
- Bottom of the object is at a greater depth than the top of the object
- Means that bottom experiences larger pressure than top
- Means there is a larger force acting on the bottom than at the top
- There is a resultant force acting upwards = upthrust
What is needed for an object to float?
Upthrust must equal object’s weight (downward force due to gravity)
What is the upthrust equal to?
The weight of fluid that has been displaced by the object
(objects weight)
What causes an object to sink?
Objects weight is more than the upthrust
If the object is more dense than the liquid
What is distance? Scalar or vector?
How far an object has moved, scalar
What is displacement? Scalar or vector?
Vector, measures the distance and direction in a straight line from an objectts starting point to its finsihing point
What is velocity?
Vector quanitity, how fast your going and direction
What is speed?
How fast your are going
Speed of person walking
1.5m/s
Speed of person running
3m/s
Speed of person cycling
6m/s
Speed of a car
25m/s
Speed of a train
30m/s
Speed of a plane
250m/s
Factos affecting speed person walk, run or cycles
- Age
- Terrain
- FItness
- Distance travelled
Typical speed of sound
330m/s
What affects wind speed?
- Temperature
- Atmospheric pressure
- Large buildings/structures nearby
- Forests reduce speed of air
What 2 things have varying speed?
Sound and wind
What is acceleration
Change in velocity in a ccertain amount of time
Formula for acceleration
A = change of velocity ÷ time taken
a = v-u/t
What does uniform acceleration mean?
Constant acceleration
Equation for uniform acceleration
v² - u² = 2as
v = final velocity
u = initial velocity
a = acceleration
s = distance
What is the acceleration of any object falling freely under gravity near the Earth’s surface?
9.8 m/s²
What does the gradient on a distance-time graph mean?
Speed
Steeper = faster
distance-time graph
Flat sections mean?
Stationary
distance-time graph
Curves mean?
Acceleration or deccleration
What does the gradient in a velocity-time graph mean?
Acceleration
velocity-time graph
Flat sections mean?
Steady speed
velocity-time graph
Curve mean?
Changing acceleration
velocity-time graph
Uphill mean?
Acceleration
velocity-time graph
Downhill mean?
Deceleration
How would you find the speed on a distance-time graph on a sloping line?
Draw tangent against line and calc gradient on drawn line
What is drag?
- Resistance you get in a fluid
- Air resistance is a type of drag
How can you reduce drag?
Keeping the shape of the object streamlined (object designed to allow fluid to flow easily across it)
How do parachutes work?
- SA increases - AR increases
- AR is greater than weight
- Resultant force upwards
- Skydiver decelerate
- As velocity has decreased, AR also decreases
- At some point, AR will balance weight so resultant force = 0
- Velocity will stay constant then
- So now skydiver is falling at a lower terminal velocity
What happens to frictional forces in fluids when speed increases?
Increases,
Process of a falling skydiver reaching terminal velocity
- Skydiver jumps out of plane - only force is weight
- Weight due to gravity - wont change
- Due to weight, skydiver experiences resultant force acting downwards so they accelerate downwards
- Experiences friction with air molecules - air resistance acts upwards
- Weight is greater than air resistance so continues accelerating downards
- As velocity increases, AR increases too
- At a certain point, AR balances weight
- Now there is no resultant force, so velocity stays constant
- Has reached terminal velocity
What is Newtons First Law?
- Resultant force on stationary object is 0 = stationary
- Resultant force on moving object is 0 = move at same velocity
- A resultant force is required to change the motion of an object
How can the velocity of an object change?
If there is a resultant force acting on it that is not 0
Formula for Newton’s 2nd Law
F = ma
Resultant force (N) = mass (kg) X acceleration (m/s2)
What is Newton’s 2nd Law?
- Non-0 resultant force acts on an object = accelerate
- A resultant force will cause an object to accelerate in the direction of the force.
What is an object’s inertial mass?
How difficult it is to change the velocity of the object
What is inertia?
Objects will stay stationary or carry on moving at a steady speed/motion until a resultant force is applied
How is the inertial mass defined as?
Ratio of force over acceleration
What does an object with a larger interial mass need?
Larger force produce a given accelration compared to an object with a smaller interial mass
What is Newton’s 3rd Law?
When 2 object interact, the forces they exert on each other are equal and opposite
What affects the size of air resistance if a person is falling from the air
- SA of person - higher area = larger the area over which collisions can take place
- Veolcity person is moving - faster = more particles collide with
What is a normal contact force?
Chair exerts a force on the ground, ground pushes back the chair with the same force. Equal but opposite are felt by both
What does the spring constant mean?
How many newtons it would take to stretch the object by 1m
What is Hooke’s Law?
When does it stop being applied?
- Force and extension is directly prop.
- Stops after limit of proportionality/elastic limit, onject will be inelasticly deformed, wont return to original shape
What does extension in a spring mean?
Increase or decrease when its stretched or compressed
On a force-extension graph, what does the straight part’s gradient of the graph mean?
Gradient = k - spring constant
What does the area under the curve of a force-extension graph mean?
Energy transferred
What does the ozone layer do?
Keeps out most harmful radiation
Where is the density of gas particles the highest on Earth?
On the Eath’s surface, pressure gets smaller the further you get
Why is there a greater atmospheric pressure at sea level than at higher elevation?
- Air is more dense at sea level
- More gas particles at sea level to collide with objects
- Higher atmos. pressure
On a distance/time graph, where is the distance and time?
Distance- y-axis
Time - X-axis
How would you find the distance trvalled on a velocity/time graph?
Calc area under it
What increases air resistance when a person is falling
- Larger sa - LARGER area over which collisions can take place
- velocity - faster they are moving, more collisions
What is an emergency stop?
Where max force applies by brakes in order to stop car in the shortest possible distance
What is the stopping distance?
Thinking distacnce + breaking distance
What is the thinking distance?
How far car travels during drivers reaction time
What is breaking distance?
Distance taken to stop under the braking force
What is thinking distance affcted by and how?
- Speed - the faster you’re going, further you’ll need to travel during the time you take to react
- Your reaction time - longer ur reaction time, longer ur thinking distance
What is breaking distance affected by and how?
- Ur speed - faster travelling = longer it takes to stop
- Weather or road surface - wet/icy road reduces friction = skidding, if tyres are bald they cant get rid of water in wet conditions
- How good brakes are - if worn or faulty, wont be able to apply as much force as good brakes, dangerous
Factors affecting stopping distance and how this affects safety?
- Icy roads - increases skidding, so driving too close to other cards in icy conditions is usafe
- Longer ur stopping distance, the more space u need to leave in front in order to stop safely
- Speed limits vital cuz speed affects stopping distance a lot
What happens when a brake is pushed?
- Causes brake pads to be pressed onto the wheels
- Contact causes friction, causes work to be done
- WD between brakes and wheels transfers energy to kinetic energy stores of wheels and thermal stores of brakes
- Brakes increase in temp
What happens as a vehicle is going faster?
- has more energy in kinetic store
- so more work needs to be done to stop it
- means a greater braking force needed to make it stop withing a certain distance
What does a larger braking force mean?
- Larger deceleration
- dangerous - may cause brakes to overheat (not work well) or skidding
What is momentum?
- Vector quantity
- Greater the mass or velocity, more momentum it has
formula for momentum
p =mv
momentum kgm/s = mass (g) X velocity (m/s)
What is the conservation of momentum?
In a closed system, total momentum before an events = after event
What does a positive momentum mean?
Objects going to the right
Formula linked with force, change in momentum
F = change in momentum / time
What does a larger force do to the momentum?
larger force = faster change in momentum
What happens if the momentum changes v quickly in a car?
- forces on the body will be v large
- causes injury
What does it mean when it takes longer for momentum to change? eg car
- longer for momentum to change
- means smaller rate of change of momentum
- so smaller force
- small forces= injuries less severe
Car safety features to lengthen time of momentum change and explain
- crumple zones - crumple of impact, increasing time taken for car to stop
- Seat belts stretch a bit - increasing tt for wearer to stop
- Air bags inflate before u hit dashboard - comprssing air inside it slows u down more gradually
other ways to minimise force by lengthening time for change in momentum
- bike helmets - contain crushable layer of foam - lengthens time taken for ur head to stop in a crash - reduces impact on ur brain
- crash mats and cushioned playground flooring - increase tt for u to stop if u fall on them - cuz they are made from soft, compressinle materials
equipment for rp 6 stretching a spring
- clamp stand
- 2 bosses
- 2 clamps
- heavy weighht
- metre rule
- spring
method for rp 6 stretching a spring
- Set up clamp stand, 2 bosses and 2 clamps
- Place heavy weight on clamp stand to stop it falling over
- attach metre rule and spring
- top of spring must be at the 0 point on metre rule
- metre rule must be vertical
- bottom of spring has wooden splint attached as a pointer
- read unstretched spring length
- Hang a 1N weight on spring
- read new position of pointer on metrerule
- carry on adding weights
- work out extension produced by each weight (substract by unstrecthed weight)
- plot extension against weight
Aparatus for rp 7 acceleration
- Toy car
- string
- pulley
- 100g mass
- timer
Why is it better to use a line graph instead of a bar chart for velocity and time?
Velocity and time are both continous variables
When a car drives, how does the forces of frictional force and driving force change during the first 2 sec?
Driving force increases, as speed increases, frictional force increases, driving force is still greater than frictional force
If a car is experiencing an 800N force, backwards and forwards, what is it doing?
Moving at a constant speed
Factors affecting thinking distance
alcohol
drugs
tiredness
care safety features
- seat belts
- crumple zones
- air bags
