P3- Forces For Transport Flashcards
What are distance time graphs?
They allow a collection of data to be shown. It is easier to interpret data agent hey are plotted on a graph than when they are listed in a results table.
What does increasing speed mean?
Increasing the distance travelled in the same time.
Increasing the speed reduced the time needed to cover the same distance.
What does the gradient of a distance time graph tell you?
The speed of the object
The higher the speed, the steeper the gradient.
In a distance time graph what does a straight diagonal line indicate?
The speed is constant.
In a distance time graph what does a curved line show?
The speed is changing.
What is acceleration?
A change of speed per unit of time.
If the speed is increasing,what is the object doing?
Accelerating
In a speed time graph, how can you work out distance travelled?
The area under the graph.
What is acceleration measured in?
m/s^2
What does a negative acceleration show?
The car is decelerating.
In distance time graphs what does a straight line mean?
Stationary
In speed time graphs, what does a straight line mean?
It’s speed is constant.
What is velocity?
A vector.
It has both speed and direction.
When two cars are moving past each other, their RELATIVE velocity is..
The sum of their individual velocities if they are going in opposite directions.
The difference of their individual velocities if they are going in the same direction.
A vehicle may go around a roundabout at a constant speed but…
It is accelerating. This is because it’s direction of travel is changing. It’s not going in a straight line. The driver needs to all,y a force towards the centre of the roundabout to change direction. This give the vehicle an acceleration. Directed towards the centre of the roundabout.
Any object moving along a circular Path moves at a…
Tangent to the circle.
If the forces acting on an object are balanced shay does this mean?
It is at rest. Whereas if the forces are unbalanced, it’s speeds up or slows down.
What is the unit of force?
Newton (N)
What is f=ma
Force= Mass x acceleration
Reaction time will increase if…
The driver is tired, under the influence of alcohol or other drugs, travelling faster, distracted or lacks concentration.
Breaking distance may increase if,,,
The road conditions are poor eg icy
The car has not been properly maintained, eg worn breaks.
The speed is increased.
For safe driving, it is important to stop safety by..
Keeping an appropriate distance from the car In front
Having different speed limits for different types of roads and locations
Slow down when road conditions are poor
Factors affecting breaking distance are…(5)
-the grater the mass of a vehicle, the greater it’s breaking distance
-the greater the speed of a vehicle, the reader it’s breaking distance
When the breaks are app,odd the break pads are pushed against the disc. This creates a large friction force that slows the car down. Worm breaks reduce the friction force, increasing the breaking distance.
-worn tyres with very little tread reduce the grip of the wheels on a slippery road, leading to skidding and an increase in breaking distance.
-increased breaking force reduces the stopping distance.
Thinking distances increases _____ with speed.
Linearly
Breaking distance increases as a ……
Squared relationship
Work is done when…
A force moves an object in the direction in which force acts.
Weight is a measure of…
Gravitational attraction on a body acting towards the centre of the earth.
A mass of 1kg has a weight of… On earth
10 N
Power is ..
The rate at which work is done
A persons power is greater when…
They run or walk
Explain powerful cars
Some cars are more powerful than others. They travel faster and cover the same distance in a shorter time and require more fuel. The power rating of a car depends on its engine size. More powerful cars have greater fuel consumption.
Why is a car with a high fuel consumption expensive to run?
Because fuel is expensive
How does fuel pollute the environment?
Cat exhaust gases, especially carbon dioxide are harmful.
Carbon dioxide is also a major source of greenhouse gasses, which contribute to climate change.
The breaking distance of a car increases with increasing speed, but…
Not proportionally.
When a car stops, what happens to it’s kinetic energy?
It changes Into heat in the breaks, tyres and road.
What happens when the speed of a car doubles?
The kinetic energy and the breaking distance quadruple. This is why there are speed limits and penalties for drivers who exceed them.
Fuel consumption data are based on…
Ideal road conditions for a car driven at a steady speed in urban and non urban conditions.
Factors that effect the fuel consumption of a car are…. (5)
The amount of energy required to increase it’s kinetic energy
The amount of energy required for it to do work against friction
It’s speed
How it is driven, such as excessive acceleration and deceleration, constant breaking and speed changes
Road condition, such as a rough surface
Electric cars are battery driven or solar powered, how do they work…
The battery takes up a lot of room
They have limited range before recharging
They are expensive to buy but the cost of recharging is low
Solar powered card rely on the sun shining and need backup batteries.
Exhaust fumes from petrol fuelled And diesel fuelled cars cause..
Serious pollution in towns and cities
Batteries driven cars do not pollute the local environment but…
Their batteries need to be recharged. Recharging uses electricity from a power station. Power stations pollute the local atmosphere and cause acid rain.
So,ar powered cars do not produce…
Carbon dioxide emissions
Biofuels may reduce carbon dioxide emission but…
This is not certain because deforestation leads to an increase in carbon dioxide levels.
Spreading the momentum change over a longer time reduces what?
The force
To minimise injury, forces acting on the people during an accident must what…
Be minimised
Force can be reduced by reducing the acceleration. This can be done by…
Increasing stopping or collision time
Increasing stopping or collision distance.
What are important safety features in a car?
Crumple zones Seat belts Air bags Crash barriers Escape lanes
Modern cars have safety features that ________ _______ when a vehicle stops suddenly.
Absorb energy
How do safety features absorb energy? (4)
Breaks get hot
Crumple zones that change shape
Seat belts that stretch a little
Air bags that inflate and squash
On impact, what do crumple zones, seat belts and air bags do?
Crumple zones
At the front and rear of the car absorb some of its energy by changing shape or crumpling
Seat belts
Stretch a little so that some of the persons kinetic energy is converted to elastic energy
Air bags
Absorb some of the person’s kinetic energy by squashing up around them
What do all the safety features do?
Absorb energy
Change shape
Reduce injuries
Reduce momentum to zero slowly, therefore reducing the force on the occupants.
Some people don’t like wearing seat belts because…
There is a risk of chest injury
They may be trapped in a fire
Drivers may be encouraged to drive less carefully because they know they have the protection from a seat belt.
Despite computer modelling, crash tests using real vehicles and dummies provide…
More safety information
What are ABS breaks?
A primary safety feature which helps to prevent a crash.
All objects fall with the same acceleration due to gravity as long as…
The effect of air resistance is very small
The size or the air resistance force on a falling object depends on…
It’s cross sectional area, the larger the area the greater the resistance
It’s speed, the faster it falls the greater the air resistance
Air resistance has a significant effect on motion only when…
It is large compared to the weight of the falling object.
How does a parachutist fall?
1) the parachutist accelerates, displacing more air molecules every second. The air resistance force increases. This reduces his acceleration. So the higher the speed, the more air resistance.
2) the parachutists weight is equal to the air resistance, the forces on him are balanced. He travels at a constant speed, terminal speed
3) when the parachute opens, the upward force increases suddenly as there is a much larger surface area, displacing more air molecules each second. So, the larger the surface area, the more air resistance. The parachutist decelerates, displacing fewer air molecules each second so the air resistance force decreases.
4) the parachutist reaches a new slower terminal speed when his weight is equal to the air resistance once more, so he lands safetly.
What else can use parachutes to slow them down?
Drag racers and space shuttles.
The force on each kilogram of mass due to gravity is…
g= 10N/kg
What is the figure of the acceleration due to gravity?
g= 10m/s^2
How can the gravitational field strength vary and unaffected by?
Varies with position on the earths surface. (Closer to the core)
Varies with height above or depth below the earths surface.
Is unaffected by atmospheric condition.
An object held above the ground has…
Gravitational potential energy
GPE=MGH=KE
you should know this
How does a roller coaster work?
Uses a motor to haul the train up in the air. The riders at the top of the ride have a lot of gravitational potential energy. When the train is released it converts gravitational potential energy to KE as it falls. Each peak is lower than the one before because some energy is transferred to heya and sound due to friction and air resistance.
If speed doubles, KE…
Quadruples
If mass doubles…
KE doubles
