Topic 1 - Forces and Motion Flashcards
What is a force? What can it change?
A force is a push or a pull, it can change the speed, direction or shape of an object
What is the difference between scalars and vectors?
Vectors have size (magnitude) and direction, scalars have size but no direction
Hooke’s law is F = K x E, but what are the units, and how is it rearranged?
F = Force (N)
K = Spring Constant (N/m)
E = Extension (m)
F = k x e
K = F / e
E = F / k
What does spring constant measure?
How hard it is to stretch or compress a spring, the larger the spring constant the harder it is to compress/stretch
Under what circumstances does Hooke’s law NOT apply?
When the limit of proportionality is exceeded
- What is elasticity?
- What is elastic deformation?
- The ability to regain shape after deforming forces are removed.
- When a material returns to it’s original shape when forces are removed
What are Newton’s 1st, 2nd and 3rd laws?
1st: When an object is at rest, it remains at rest
When an object is moving, it remains moving at a constant velocity in a straight line (unless resultant force acts on it)
2nd: F = ma (Force - N - = Mass - kg - X Acceleration - m/s^2)
3rd: Every force has an equal and opposite force (the forces are the same type but act on different objects) - e.g. two balls hit each other, they will bounce off each other due to the opposite force
What does Zero, The gradient, and a horizontal line represent on a distance-time graph?
Zero: The origin, the object has not moved from the starting point
The gradient: The speed of movement
A horizontal line - The object is stationary
What does Zero, The gradient, and a horizontal line represent on a velocity-time graph?
Zero: No movement
The gradient: Acceleration
Horizontal line: Constant speed
How does a speed camera measure the speed of a car?
It looks at how long it takes for the cars to take going between lines of a known distance.
What does the area under a velocity-time graph equal?
The distance travelled
The equation for acceleration is a = △V / T, but what are the units, what can this equation also be known as, and how is it rearranged?
t = time (s)
△v = m/s (△ means change in)
a = acceleration (m/s^2)
It can also be known as a = v-u/t
v = Final velocity
u = Original velocity
Rearranged:
△v = a X t
t = △v / a
What is the equation for stopping distance?
Stopping distance = Thinking distance + Braking distance
What is thinking distance?
The distance a vehicle travels during the drivers reaction time (before the brakes have been applied)
What is braking distance?
The distance a vehicle travels between the brakes being applied and the vehicle coming to a complete stop (under the braking force)
What is thinking distance directly proportional to?
Speed, as speed doubles, thinking distance doubles.
What is the relationship between braking distance and speed?
Braking distance = speed ^ 2, as speed doubles, braking distance quadruples
What is drag dependent on?
Surface area
Streamlining
Speed
What are the units and rerrangements of v^2 - u^2 = 2as?
v = Final velocity (m/s)
u = Initial velocity (m/s)
a = acceleration (m/s^2)
s = Distance/displacement (m)
v = √2as+u^2 (All Rooted)
u = √v^2-2as (All Rooted)
a = v^2 - u^2 / 2s
s = v^2 - u^2 / 2a
What is momentum?
The tendency of an object to keep moving
Momentum is p = m x v, but what are the units and rearrangements?
p = momentum (kgm/s)
m = mass (kg)
v = velocity (m/s)
m = p/v
v = p/m
In a closed system, what momentum law is there?
The momentum before is equivalent to the momentum after - This is called conservation of momentum.
What is an explosion
An event caused when stored energy is suddenly transferred into kinetic energy
What are 3 examples of the conservation of momentum?
Car crashes, balls hitting each other and explosions
F = m △v / △t, but what are the units and rearrangements?
F = Force (N)
m = Mass (kg)
△v = change in velocity (m/s)
△t = change in time / time taken (s)
△t = m △v / F
v = F △t / m
m = F △t / △v
1.Name three car safety features
- How do they work?
- Seat Belts
Crumple Zones
Air bags - They increase the time taken for a collision, which means that the force is reduced
How does increasing time taken to stop/for a collision to take place, reduce the impact force?
- Increases the time taken to stop
- Therefore decreases the rate of change of momentum
- And so the impact force is reduced
The equation is m = f x d, but what are the units and rearrangements?
M = moments (Nm)
f = Force (N)
D = Distance (m)
What is different about the m = f x d equation in it’s answer to other equations?
As moments are around a point/lever, direction must be states (anticlockwise/clockwise)
What is the principle of moments?
For an object in equilibrium, the sum of all the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.
