Topic 5 - Forces Flashcards
What is a vector quantity?
it has magnitude and direction
Give examples of vector quantities (5)
- force
- velocity
- displacement
- acceleration
- momentum
What is a scalar quantity?
only has magnitude and no direction
Give examples of scalar quantities (7)
- mass
- speed
- distance
- time
- energy
- power
- density
What is the equation to calculate weight?
mass x gravity
What will happen to an object with NO resultant force acting on it?
either:
- remain stationary
- remain at a constant velocity
What will happen to an object with a resultant force acting on it?
accelerate - it could be:
- speeding up
- slowing down
- changing direction
Define a resultant force
one force representing multiple forces
Define elastic deformation
the object can go back to its original shape after the force has been removed
Define inelastic deformation
the object cannot go back to its original shape - it has been permanently deformed
When does inelastic deformation occur?
when the limit of proportionality is exceeded
What is Hooke’s Law?
The extension of an object is directly proportional to the force applied to it, provided the limit of proportionality hasn’t been exceeded
What is the law of conservation of energy?
energy cannot be created or destroyed, only transferred
A moment depends on 2 things:
- the perpendicular force
- the perpendicular distance
What is the principle of moments?
for a system in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments
What is a moment?
the turning effect of a force
Define speed
the rate of change of position
Define velocity
the rate of change of position in a given direction
What is the average walking speed?
1.5 m/s
What is the average running speed?
3 m/s
What is the average cycling speed?
6 m/s
Define acceleration
the change in velocity in a certain amount of time
On a velocity-time graph, what does the gradient of the line represent?
acceleration
On a distance-time graph, what does the gradient of the line represent?
speed
How do you find distance on a velocity-time graph?
the area under the graph
What is drag?
the resistance you get in a fluid
How do you reduce drag?
keeping the shape of the object streamlined
Why will an object slow down and stop if it has no force propelling it?
friction
Describe an object falling
- when it first sets off, the force of gravity is much more than the frictional force slowing it down, so it accelerates
- as the speed increases, the friction builds up
- this gradually reduces the acceleration until the frictional force is equal to the accelerating force (so the resultant force is zero)
- it will have reached its terminal velocity and will fall at a steady speed
Define terminal velocity
the maximum speed of an object, reached when the forces moving the object are balanced by its frictional forces
Name Newton’s 1st law
if an object has no resultant force, it will continue to move at a constant velocity or remain stationary
Name Newton’s 2nd law
resultant force = mass x acceleration
- acceleration is directly proportional to the resultant force
- acceleration is inversely proportional to the mass
Name Newton’s 3rd law
when two objects interact, the forces they exert on each other are equal and opposite
Define stopping distance
- the distance travelled between seeing the obstacle and the car reaching 0 m/s
- thinking distance + braking distance
Define thinking distance
the DISTANCE travelled between seeing the obstacle and applying the brakes
Define braking distance
the DISTANCE travelled between applying the brakes and the car reaching 0 m/s
Factors affecting thinking distance:
- tiredness
- drugs/alcohol
- distractions
Factors affecting braking distance:
- speed
- road conditions
- vehicle conditions
Describe how you investigate how mass affects acceleration
- set up the ramp on the lowest setting
- attach a piece of card on to the top of the trolley
- find the mass of the trolley
- fasten the pulley to the end of the bench and set up the string
- set up 2 light gates - one near the top and one near the bottom of the ramp
- put a mass at the end of the string
- release the trolley from the top of the ramp and record the speed as it passes through each light gate (using a data logger)
- repeat adding 100g mass each time
What is the relationship between mass and acceleration?
when mass increases, acceleration decreases (inversely proportional)
Describe how you would investigate how force affects acceleration
- set up the ramp, attach a piece of card to the top of the trolley, find the mass of the trolley
- fasten the pulley to the end of the bench and set up the string, set up 2 light gates at the top and bottom of the ramp
- add 5 masses to the mass holder on the end of the string
- release the trolley and record the time passing through each light gate
- remove one mass from the stack and add it to the top of the trolley (will keep the total mass constant)
- repeat for each further mass on the stack
What is the relationship between force and acceleration?
as force increases, acceleration increases
(directly proportional)
Define inertial mass
the ratio of force to acceleration
Define momentum
Momentum is a quantity of a moving body that is proportional to its mass and velocity - how difficult the object is to stop
What is conservation of momentum?
In a closed system, the total momentum before an event is the same as after the event.
Why are cars designed to slow people down over a longer period of time?
- a longer time means a smaller resultant force because there’s a reduced rate of change of momentum
- this means the force is smaller so less chance of injury
