Topic 2 - Motion and forces Flashcards
(40 cards)
Describe a scalar quantity
A scalar quantity has just magnitude
Describe a vector quantity
A vector quantity has both magnitude and a specific direction
Explain the difference between vector and scalar quantities
Generally, scalar cannot be negative, but vectors can be, as a certain direction is positive
Give examples of vector/scalar quantities
Scalar:
-Speed
-Distance
-Time
-Mass
-Energy
Vector:
-Velocity
-Displacement
-Acceleration
-Force
-Momentum
What is the equation for speed?
(average) speed (metre per second, m/s) = distance (metre, m) ÷ time (s)
Describe velocity
Velocity is speed in a stated direction
What is the equation for distance travelled?
distance travelled (metre, m) = average speed (metre per second, m/s) × time (s)
Describe Distance Time graphs
The gradient is velocity.
The sharper the gradient means faster speed.
A negative gradient is returning back to the starting point.
A horizontal line means stationary.
0 distance means that it is back to the starting point.
Curved line means the velocity is changing (acceleration).
What is the equation for acceleration?
acceleration (metre per second squared, m/s²) = change in velocity (metre per second, m/s) ÷ time taken (second, s)
a = v-u ÷ t
What is the equation which uses change in velocity?
(final velocity)² (m/s)²) – (initial velocity)² (m/s)²) = 2 × acceleration ( m/s²) × distance (metre, m)
v²-u² = 2ax
Describe Velocity Time Graphs
Gradient is acceleration.
Sharper gradient means greater acceleration.
Negative gradient is deceleration.
Horizontal line, constant speed.
0 velocity means that it is stationary.
Area under line = distance travelled.
Curved line means that the acceleration is changing.
How do you determine constant speeds?
Measure distance travelled.
Use stopwatch for time taken.
Use speed = distance/time
How do you determine average speed?
Work out total distance travelled.
Find the time taken for the whole journey.
Use speed = distance/time
How do you determine speeds using light gates? Why is this more accurate than other methods?
Set up two, one at start and one at end.
Measure distance between them.
As soon as the object passes through the first, it will measure the time taken to reach the second.
Then use speed = distance/time
This is more accurate as it removes reaction time and human error with a stopwatch.
What are the typical speeds for wind, sound, walking, running, cycling, train and plane?
Walking= 5km/h = 1.4m/s
Running= 6mph = 3m/s
Cycling= 15km/h = 6m/s
Wind = 5-7m/s
Train= 125 miles/h = 56m/s
Plane= 900km/h= 250m/s
Sound= 330ms⎺¹
What is acceleration in freefall?
10m/s²
What is Newton’s first law?
An object has a constant velocity unless acted on by a resultant force
If a resultant force acts on an object how will it react based on Newton’s first law?
It will accelerate. Acceleration is change in velocity over time so the velocity will change. So the direction or speed of the object will change (or both).
If the resultant force is zero how will an object react based on Newton’s first law?
There will be no acceleration so it will move at constant velocity (same speed and direction).
If the object is a rest there is no speed.
What is Newton’s second law as an equation?
force (newton, N) = mass (kilogram, kg) × acceleration (metre per second squared, m/s²)
F = m*a
What is the equation for weight?
weight (newton, N) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg)
W = m*g
How is weight measured?
Using a force meter, or weighing scales and is used to work out the mass of an unknown object.
Describe the relationship between the weight of a body and the gravitational field strength
The greater the gravitational field strength, the greater the weight.
Describe the core practical to investigate the relationship between force, mass and acceleration by varying the masses added to trolleys
-Cut an interrupt card to a known length (such as 10 cm) and attach it to an air track glider.
-Set up a string attached to the glider with a bench pulley at the end of a tube and a weight hanging down over the pulley. 2 light gates should be on the glider’s path. Attach an air blower (e.g. vacuum). Make sure that the air track is level, and that the card will pass through both gates before the masses strike the floor.
-Set the data logging software to calculate acceleration.
-Use scales to measure the total mass of the glider, trolley, string and weight stack. Record this value.
Attach the full weight stack (6 x 10g masses) to the end of the string.
-Make sure the glider is in position and switch on the air blower. The glider should accelerate.
-Remove one weight and attach it to the glider using blu-tack. This will keep the total mass constant. (The weight stack is being accelerated too.)
-Repeat steps 6-7 removing one weight from the stack each time. Remember to attach each weight to the glider as it is removed from the weight stack.
-use light gates to measure acceleration and suspend weights from weight hanger to produce force and use a sloping runway
