Forces and Motion Flashcards
Units for acceleration due to gravity
m/s2 or N/kg
What is a vector quantity
A quantity with a magnitude and direction eg. velocity
What is a scalar quantity
A quantity that has a magnitude but no direction eg. mass
What is acceleration measured in?
m/s2
What is Newton’s first law?
An object will stay at rest or continue to move at a constant speed in the same direction unless acted upon by a resultant force
How do you find the resultant force of two objects?
Find the difference between both forces
What factors affect the thinking distance of a person in a car?
Alchohol
Poor visibility
Old age
Tiredness
Drugs
What factors can affect the stopping distance of a car?
- Its mass
- Its speed
- The driver’s reaction time
- The condition of the brakes
- The road conditions
- Amount of friction between the tyres and road
What is speed?
How fast an object is moving
What is velocity?
Speed in a certain direction
What is distance?
How far something has or will travel
What is displacement?
Distance in one direction as the fastest route
Give some examples of vector quantities
- All forces (eg. Weight)
- Velocity
- Displacement values
Give some examples of scalar quantities
- Energy
- Speed
- Mass
How are vector quantities shown on diagrams?
With arrows
What does a flat line mean on a distance time graph?
The object is stationary
What does a curve represent on a distance time graph?
Acceleration or deceleration
What does a straight line mean on a distance time graph?
Object is stationary
What does a flat line mean on a velocity time graph?
The object is travelling at a constant speed
What does a diagonal line mean on a velocity time graph?
Acceleration or deceleration
How do you find the distance travelled in a velocity time graph?
You work out the area under the graph
How do you work out the acceleration on a velocity time graph?
Use the equation
Describe an object’s motion if the resultant force is 0
Either:
- It will be travelling at a constant speed
- It will be stationary
What different resistive forces could be acting on a car when in motion?
- Air resistance
- Friction
- Contact force
What is terminal velocity?
The maximum velocity of an object, reached when the forces moving the object are balanced by its frictional forces
What is thrust?
A force used to move something forwards or up
What are balanced forces?
When the resultant force is 0
If two forces are balanced, what is the resultant force?
0
Is the moon travelling at a constant velocity?
No, because is not moving in a constant direction
What is constant velocity?
When something is travelling at a constant speed in a constant direction
What is the name of the force bringing something forward?
Driving force
What is Newton’s second law?
F = ma
What is inertial mass?
The ratio of force over acceleration
m = F/a
What is Newton’s third law?
For every action there is an equal and opposite reaction
What are the 4 criteria for Newton’s third law pairs?
The forces must be:
- Equal in magnitude
- Acting in the opposite direction
- The same type of force
- Acting on different objects
Give an example of a Newton third law pair
The gravitational force of the Earth on the Moon
and
The gravitational force of the Moon on the Earth
Stopping distance = ???
Thinking distance + braking distance
What factors affect the braking distance of a car?
- Its mass
- Its speed
- The condition of the brakes
- The condition of the road
- The amount of friction between the tyre and the road surface
What factors affect a drivers reaction time (thinking distance)?
- Age
- Alcohol or drugs
- Poor visibility
- Tiredness
- Distractions
What is the equation for momentum?
Momentum = mass x velocity
What are the units for momentum?
Kg m/s
What is the conservation of momentum?
The principal that in a collision the total momentum before the event is equal to the total momentum after the event.
How does a crumple zone help in a car crash.
A crumple zone will change the shape of a car during a crash. If the change in momentum happens over a longer time, there is less force, shown by the equation F = mv-mu/t
What is the typical speed of sound?
330 m/s
What is the typical cycling speed of a person?
6 m/s
What is the typical running speed for a person?
3 m/s
What is free fall?
The acceleration due to gravity
Name 3 car safely features designed to reduce the time of a collision
- Seat belts
- Air bags
- Crumple zones
How do wet roads affect the stopping distance of a car?
Increases braking distance as wet roads reduce friction between the road and the car tyres
What is centripetal force?
The resultant force of an object travelling in a circle, acting towards the centre of the circle
Describe the relationship between the rate of change of momentum and the force
They are directly proportional
How do you calculate the braking distance of a car?
- Find the work done (E) to stop it
- This is the same the kinetic energy of the car (1/2mv2)
How do you calculate gear ratio?
Amount of teeth on driven gear
———————————————
Amount of teeth on driver gear
What is a moment?
A turning force
Which of these will be able to cut through tougher stuff and why:
- Long handled scissors
- Short handled scissors
The longer handled scissors, because the distance normal to the direction of the force is directly proportional to the moment
Describe the relationship between clockwise and anticlockwise moments when an object is at equilibrium
The sum of clockwise moments = The sum of anti-clockwise
Name two methods for determining the speed of an object
- Dropping a ball from a height of 1m and measuring the time taken
- Using light gates
What is the typical speed of a car?
10-30 m/s
What is the typical speed of a plane?
200-250 m/s
What is the acceleration in free fall?
10 m/s2
Describe an object’s motion if the resultant force is not 0
It accelerating/decelerating and/or changing direction
What is weight?
The force due to gravity on an object
Describe the relationship between the weight of an object and the gravitational field strength
They are directly proportional
How does a higher speed affect the stopping distance of a car?
The faster the car is travelling, the larger the breaking distance
