Topic 2 + 3 - Forces Flashcards
Newton’s first law (3)
If zero resultant force acts on stationary object, object doesn’t move
If zero resultant force acts on moving object, it continues moving at same velocity
If non-zero resultant force acts on object, object accelerates in direction of force
Newtons 2nd law (equation)
F=ma
F= resultant force (N)
M= mass (kg)
A= acceleration (m/s²)
Newton’s second law
Acceleration is directly proportional to resultant force
Acceleration is inversely proportional to mass
Newtons 3rd law
Two interacting object exert equal and opposite forces on each other
What is weight? (+equation)
Force that acts on an object due to gravity
W=mg
How to measure weight?
With calibrated spring-balancer (newtonmetre)
What is the centre of mass?
The point at which an objects weight appears to act
What does object weight depend on?
Strength of gravitational field at object location
True or false: object mass has same value anywhere in the universe
True
What is inertial mass?
Measure of how hard it is to change an object’s velocity. It’s the ratio of force over acceleration
True or false: the bigger the inertial mass, the harder it is to increase velocity
True
What happens to an object in circular motion?
It’s always changing direction, so object has changing velocity
Changing velocity means object is accelerating, so there’s a resultant force on it
What is the centripetal force?
It always acts towards the centre of the circle.
What does mass do to momentum?
The greater the mass the greater the momentum.
What does velocity do to momentum?
The greater an objects velocity, the greater its momentum
Momentum (equation)
P=mv
P= momentum (kg m/s)
M= mass (kg)
V= velocity (m/s)
What is conversion of momentum?
In a closed system, total momentum before an event equals total momentum after an event
Typical human reaction time
0.2-0.9 s
Factors affecting reaction times (3)
Tiredness, drugs/alcohol, distractions
Steps to ruler drop test:
- Get someone to hold ruler so zero is between your thumb and forefinger
- Ruler dropped without warning. Catch it as quickly as possible
- Use distance ruler fell to calculate reaction time
- The longer the distance the longer the reaction time
Stopping distance (equation)
Stopping distance = thinking distance + braking distance
Factors that increase thinking distance (2)
Faster vehicle speed, long driver reaction times
Factors that increase braking distance (4)
Faster vehicle speed, heavier vehicle, poor/wet/icy road surface, damaged or worn brakes/tyres
What happens to thinking and braking distance if speed doubles
It quadruples
Work done
1/2 x m x v² = F x d
For car to stop, work done by brakes equals energy in cars kinetic energy store
True or false: the faster a vehicle is going, the greater the braking force needed to make it stop in a certain distance.
True
What does a larger braking force mean?
Larger deceleration
What can very large deceleration cause? (2)
Brakes to overheat, vehicle to skid
