TOPIC 1- Motion, Forces and Conservation of Energy Flashcards
VECTOR
A quantity with a magnitude and a direction. Can be given as a bearing.
Eg: force, acceleration, velocity, displacement, weight, momentum
Scalar
A quantity with a magnitude but no direction.
Eg: speed, distance, mass energy, temp
Difference between velocity and speed
Velocity is a vector while speed is a scalar. This is because while velocity has a magnitude and direction, speed is simply a magnitude. For example, 2 objects could be travelling at the same speed but at different velocities.
Velocity
Speed in a stated direction
Average Speed equation
Distance travelled/time
M and s
Typical speed of walking Running Cycling Cars on a motorway Aeroplane
1.5m/s 3m/s 6m/s 30m/s 250m/s
What’s centripetal force?
When an object is travelling at a constant speed but is constantly changing direction (velocity), a force acts inwards on the object.
Speed of sound in air
340m/s
Acceleration equation
V-u/ t
Change in velocity/ time
Deceleration
Negative acceleration
Acceleration of gravity in free fall
10m/s^2
What’s acceleration measured in?
M/s^2
Uniform acceleration and its equation
Constant acceleration V squared - u squared = 2 * a * x X = distance A= acceleration V = final velocity U = initial velocity
How do you find the speed of an object in distance time graphs?
Gradient
Change in y/change in x
What do curves show on distance time graphs?
Acceleration
What do you do if the graph is curved?
Draw a tangent and find the gradient of the tangent
How do you find the acceleration on velocity time graphs?
Gradient
What does a curve represent on a velocity time graph?
Change in acceleration
How to find distance travelled on a velocity time graph
Area underneath the graph
What can you use to measure the speed of objects?
Use a stopwatch (human error) over a set distance.
Use a light gate.
Video it
Data logger
Distance
How far a quantity has moved.
SCALAR
Displacement
Distance and direction in a straight line from an object’s starting point to its finishing point.
Speed
How fast you are going
SCALAR
Distance travelled=
(Average) speed * time
Acceleration definition
Change in velocity over a period of time
Uniform acceleration
Constant acceleration
Newton’s first law
If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it will just carry on moving at the same velocity.
5 forms of acceleration
Starting Stopping Slowing Speeding up Changing direction
Relationship between force and acceleration
Directly proportional
Acceleration and object mass relationship
Inversely proportional
Formula for Newton’s second law
F = m*a
Force = mass * acceleration
Why are large decelerations dangerous?
Because they require a large force (f=ma), this can be lowered by slowing down the object over a longer time.
Purpose of safety features in vehicles
To increase collision times and so reduce force which reduces risk of injury. (Eg seatbelts/airbags/crumple zones)
Weight
The force acting on an object due to gravity. Caused by gravitational field around earth.
Where does weight exert force on an object?
Its center of mass
Point at which assume whole mass is concentrated
How to measure weight?
Spring balance or Newton meter
Weight =
Mass * gravitation field strength
W = mg
How to investigate motion of trolley on ramp
Measure trolley mass, unit masses, hanging hook, card length.
Mark line on ramp before first light gate (so travels same distance every time)
Attach trolley to hanging mass w string. Let go so it rolls down slope.
Changing ramp height and recording : initial speed, final speed and time between 2 light gates.
What are light gates used for?
Short intervals to rid of human error by reaction times
What can you use to measure distance and time?
Rolling tape measure
Stop watch
Video camera
Inertial mass
The ratio of force over acceleration.
Tendency for motion to remain unchanged.