Forces and Motion Flashcards
What is a force?
Something acting in an object that can change its shape, direction and speed
What us force measured in?
Newton’s (N)
What is a vector?
A quantity with size, magnitude and direction
What is a scaler?
A quantity with only magnitude not direction
What are some types of forces?
Air resistance Gravity Electric Tension Weight Normal Thrust
What is friction?
Friction opposes movement when two solids are rubbed together
What is air resistance?
Air resistance opposes movement when an object moves through air
What is weight?
The effect gravity has on an objects mass
What is the normal force?
A force upwards from the ground - the force that stops us falling through the earth
What is Newton’s first law?
If there is no resultant force then a body remains moving at a constant velocity or it remains at rest
What happens when an object moves in a circle?
It has a constant speed but a changing velocity so is always accelerating
What is the resultant force that enables a change in direction?
The centripetal force - always points to the centre of the circle
What is mass?
The amount of matter we are made of or a measure of how difficult it is is change the velocity of an object
What is the equation for weight?
Weight = mass x gravitational field strength (W=MG)
What is Newton’s second law?
Says that acceleration is directly proportional to the resultant force and inversely proportional to the mass
What is a resultant force?
The effect of all the forces acting on an object
What is the equation for force?
Force = mass x acceleration (F=MA)
What is inertial mass of an object?
Measures how difficult it is to change the velocity of an object -resistance to motion
(The force on it divided by the acceleration)
What is the equation for acceleration?
Acceleration = change in velocity / time (A = (V-U)/T)
What happens if mass increases?
The acceleration decreases as the force always stays the same
What is Newton’s third law?
Every force that is applied has a reaction force that is equal in magnitude and opposite in direction
What does Newton’s third law apply to?
Applied to two objects at a time and are always the same force
What do action-reaction forces act on?
Different objects
What is balanced forces act on?
The same object
What is momentum?
momentum is a property if any moving object and is the product of mass and velocity
What us the equation for momentum?
Momentum = mass x velocity (P=MV)
What does momentum before equal?
Momentum before = momentum after -as momentum is conserved
In terms of velocity, what does objects moving in opposite directions mean?
Means one velocity is positive and one must be negative (doesn’t matter which)
What is reaction time?
The time between a person detecting a stimulus and their response
What is the average reaction time for a touch, audio and visual stimulus?
- 15 seconds
- 17 seconds
- 25 seconds
What us the equation for stopping distance?
Stopping distance = thinking distance + braking distance
What is thinking distance?
The distance travelled while a driver reacts to press the break pedal
What is braking distance?
The distance travelled after the break pedal is pressed until the car halts
What is the equation for change in momentum?
Change in momentum = force x time
(Triangle shape then P) = F x T
In terms of stopping distance what does having a larger mass mean?
Objects with a larger mass have a slower stopping distances as they therefore have larger momentum’s
What does more friction mean?
Faster stop
What effects thinking distance?
- eyesight
- fatigue
- intoxicated (drugs/alcohol)
- caffeine
- distractions
- illness
- speed
What affects braking distance?
- speed
- quality of breaks, car and tyres
- conditions if road/weather
- mass of the car so momentum
How can safety features in cars increase safety?
Crumple zones and are bags increase safety as they increase time and so reduce the force of impact -meaning there is less likely damage
What is a tip for scale diagrams?
- Make sure you measure not count squares and use arrows to show direction
- to work out final distance measure the line the forms the triangle
What is an alternate to scale diagrams?
Pythagoras theorem
What is inertia?
The tendency for motion to remain unchanged which links to Newton’s first law
What is the equation for speed?
Speed = distance / time
What is the SUVAT equation for uniform acceleration?
V2 - U2 = 2 x A x X
X represents distance
What are the different points on a distance time graph?
- gradient gives the speed of an object
- flat sections are where an object is stationary
- a straight line represents a constant speed
- curves represent acceleration
- a negative line shows it is decelerating
What are the different points on a velocity-time graph?
- gradient shows the acceleration
- flat sections represent a constant speed
- the steeper the graph the greater the acceleration/deceleration
- positive direction lines are acceleration and negative deceleration
- a curve represents changing acceleration
What does the area under a graph show?
- Distance travelled in that time interval
- So simply work out the area of that shape or count the squares
How do you find the gradient/speed from a curved line?
Draw a tangent to that curved point and find the gradient of that tangent
What is the centripetal force?
The resultant force of an object moving in a circular motion
-this forces acts towards the centre of the circle and helps keep that object moving
Where is the risk created by large deceleration?
This creates and extensive force as F=MA
What are stages 1 and 2 of investigating motion?
- set up your apparatus. measure the mass of the trolley, the unit masses and hanging hook. Then measure the mass of the piece of card which will interrupt the light gate beams
- adjust the height of the ramp until the trolley just starts to move
What are stages 3 and 4 of investigating motion?
- mark a line on the ramp just before the first light gate to make sure the trolley travels the same distance every time. The light gate will record the initial speed of the trolley as it begins to move
- placing the trolley at the start, attach the trolley to the hanging mass And let it go
What is stage 5 of investigating motion?
Each light gate should record the time the trolley passes through it and its speed at that time. The acceleration can then be found out through acceleration = change in speed / time
To work out the acceleration when investigation motion, what values to you need?
- Initial velocity - as the trolley passes through the first light gate
- final velocity - as the trolley passes through the second light gate
- time - the time it takes to travel the distance between the two light gates
What is an elastic and inelastic collision?
- Elastic is when both momentum and kinetic energy is conserved
- Inelastic is when momentum is conserved but not kinetic energy
Average masses?
Car = 1000kg Person = 60kg Bike = 10kg Motorbike = 250kg
Average speeds people
Walking = 1.4m/s Running = 3m/s Cycling = 5.5m/s
Average speeds transport
- cars city VS motorway = 13m/s vs 31m/s
- aeroplanes = 250m/s
- Trains = 55m/s
- Ferries =15m/s