Unit 2 - Motion And Forces Flashcards
How might someone have constant speed but a changing velocity
Changing direction
Why is acceleration a vector quantity
It has a direction and magnitude
Then a diagram, what represents the size of a force
By the length of the arrow
What is the thrust?
The push force on an object
What is the resultant force
The force on an object that creates the overall effect
Wha are balanced forces
When the resultant force equals 0
What are unbalanced forces
When the resultant forces don’t equal 0
What is Newton’s first law?
A moving object will continue to move at the same speed and direction unless an external force acts on it
A stationary object will remain at rest unless an external force acts on it
What forces change the velocity of an object
Unbalanced forces
What is the centripetal force?
A force that acts on a moving object in a circular path and is directed towards the centre which the object is circuling
What forces can make objects move in circular paths (3)
Centripetal force, gravity and friction
For a motorbike, what provides the centripetal force?
Friction between the tyres and the road
What is mass
The quantity of matter in an object
What is weight?
A measure of the pull of gravity on an object
What are the units for mass
Kg
What are the units for weight?
Newton’s (N)
How can weight be measured
Using a force meter
What is the GFS on Earth?
10N/Kg
What is the symbol equation for weight?
W = m x g
How can a skydiver stop accelerating
Air resistance increases with speed so after a few seconds, the air resistance balances her weight
What is Newton’s second law?
The acceleration in the direction of the resultant force depends on:
The size of the force
The mass of the object
What is the odd equation for force?
Force = mass x acceleration
What is the symbol equation for force
f = m x a
What is inertial mass
The force on an object divided by the acceleration the force produces
Explain the core practice - investigating acceleration
Put a trolley on a ramp and adjust the slope so it begins to move on its own.
Set up the light gates and the pulley and string.
Put a piece of card on the trolley and measure it.
Find the mass of the trolley
Put a mass at the other end of the string
Release the trolley and write down the speed from the datalogger
Write down the time for it to get from each light gate
Put a mass on top of the trolley and repeat
For the core practical - investigating acceleration, how can the experiment be altered to investigate the effect of force rather than the effect of mass?
Stack masses on the trolley and each time, transfer one to the other end of the string
What is Newton’s third law?
For every action, there is an equal and opposite reaction
What are action-reaction forces?
A pair of forces on the two interactive objects
What are 3 factors of action-reaction forces?
Same size, opposite directions and same type
What is an equilibrium situation for forces?
When nothing is moving equal forces e,g pulling a rope
What is the difference between action-reaction forces and balanced forces?
Balanced forces act on the same object (force of ground on dog and force of gravity on dog)
Action-reaction forces act on different objects (from ground on dog and on dog from ground)
Give 2 factors of action-reaction forces in a collision
Same size
Different effects due to different masses
What is momentum
A measure of the tendency of an object to keep moving or how hard it is to stop it moving
Why is momentum a vector quantity
It depends on velocity
What is the symbol equation for momentum
p = m x v
What is the second symbol equation for force involving velocity
f = mv - mu / t
What is conservation of momentum?
When moving objects collide, the total momentum from before the collision is the same as after the collision if there are no external forces
What is thinking distanc?
The distance the object travels between seeing the problem and reacting
What is the braking distance
The distance an object travels while the brakes are working to stop it moving
What is the stopping distance of a vehicle?
The sum of the thinking and braking distance
The time between a person detecting a stimulus and their response
What is the reaction time?
What can reaction times be measured using?
Computers
What can slow someone’s reaction time? (4)
If they are tired, I’ll, taking drugs or distracted
What can increase the braking distance? (2)
Friction (If the brakes are worn out)
Mass (heavier vehicle needs more force)
What is work done
The energy transferred by a force acting over a distance
What is the word equation for work done
Work done = force x distance
What is the energy stored in a moving object?
Kinetic energy
What is the word equation for kinetic energy
Kinetic energy = mass x velocity^2 / 2
When an object stops, what is the kinetic energy transferred to?
Other energy stores by the braking force
What is the kinetic energy equal to?
The work done
What are crumple zones?
Zones built into the front of a car which absorb the impact of a collision making the deceleration less
What is the use of airbags?
They increase the time it takes for a persons head to stop in a collision
What is the use of seatbelts
To hold the passenger into the car
Why is it best to increase the time for something to hit the ground for safety?
Because it reduces the force on it
What does the force in a collision depend on?
The change in momentum as the car comes to a stop
What does a negative sign show for a force?
It is acting in the opposite direction to the original direction
