Section 17 - Motion, forces and conservation of energy - Motion, forces, momentum and Newton's Laws Flashcards
Difference between vectors and scalars?
Vector quantities have a magnitude(size) and a direction.
Scalar quantities only have a magnitude
Name 3 vector quantities and 3 scalar quantities?
V - velocity, acceleration, momentum, weight, force, displacement
S - speed, distance, mass, energy, temperature, time
What is velocity?
Speed in a given direction
Equation for acceleration?
acceleration (m/s²) = change in velocity (m/s) / time (s)
a = (v - u) ÷ t
What is uniform acceleration?
Constant acceleration
Equation for uniform acceleration?
Final velocity² (m/s) - initial velocity² = 2 x acceleration (m/s²) x distance (m)
v² - u² = 2ax
In a distance time graph, what do the following mean:
- Flat section
- Steady gradient /
- Curve getting steeper
- Curve levelling off
- Flat - stopped
- Steady gradient / - steady speed
- Curve getting steeper - accelerating
- Curve levelling off - decelerating
In a velocity/time graph, what do the following mean:
- Flat section
- Uphill section /
- Downhill section \
- Curve
- Flat - steady speed
- Uphill / - acceleration
- Downhill \ - deceleration
- Curve - changing acceleration
What is Newton’s First Law?
If resultant force on a stationary object is zero, it will remain stationary. If resultant force on a moving object is zero, it’ll just carry on moving at the same velocity
What is Newton’s Second Law?
Resultant Force (N) = Mass (kg) x Acceleration (m/s²) F = m x a
What happens hen the resultant force on an object increases?
The larger the resultant force on an object, the more the object accelerates
How do safety features in vehicles protect the driver?
They are designed to increase collision times, which reduces the force and so reduces risk of injury
How do crumple zones in cars protect the driver?
Crumple up easily in a collision, increasing time taken to stop
Equation for weight?
Weight (N) = mass (kg) x gravitational field strength (N/kg)
W = m x g
What is centripetal force?
The resultant force that acts towards centre of circle and keeps something moving in a circle
Explain how an object travelling in a circle travelling at a constant speed is accelerating? Circular motion
At a constant speed, the object travelling in a circle is constantly changing direction, so it is constantly changing velocity. This means it’s accelerating
Why are light gates used to find the speed of an object?
It gets rid of human error by reaction times
What is inertia?
The tendency for motion to remain unchanged
What is inertial mass?
The measure of how difficult it is to change the velocity of an object
What is Newton’s Third Law?
When two objects interact, the forces they exert on each other are equal and opposite
Equation for momentum?
Momentum (kg m/s) = mass (kg) x velocity (m/s)
p = m x v
What is the conservation of momentum?
In a closed system, the total momentum before an event is the same after an event
Equation for force? momentum
Force (N) = change in momentum (kg m/s) / time (s)
F = (mv - mu) ÷ t
What is stopping distance made up of?
Stopping distance = thinking distance + braking distance
Two main factors that affect thinking distance? How?
Reaction time and speed of car
4 factors that affect reaction time?
Tiredness, alcohol, drugs and distractions
4 factors that affect braking distance?
Speed of car, mass of car, conditions of tire (worn or faulty), friction between tyres and road
