Forces Flashcards
What is a force?
Something that can change the motion of an object
It is measured in Newtons (N)
What 3 ‘laws’ can be used to describe all forces?
- An object will remain at rest or travelling at a constant speed unless a resultant force acts on it.
- F = MA
- Every action has an equal and opposite reaction
What is a resultant force?
The combined effect/overall effect of the forces acting on an object
What does it mean when the resultant force of an object is 0?
- If the object is at rest, it will stay at rest
- If the object is moving, it will continue doing so at the same speed and in the same direction
What does it mean if the resultant force on an object is not 0?
The object is accelerating
Therefore:
- If the object is at rest, it will accelerate in the direction of the resultant force
- If the object is moving in the same direction as the resultant force, it will accelerate in that direction
- If the object is moving in the opposite direction to the resultant force, it will decelerate
If an object is accelerating, what can it be doing?
- Speeding up
- Slowing down
- Chaning direction
What is acceleration?
Change in velocity per second (m/s2)
The can be changed by the object chaning either speed or direction
What is stopping distance?
Thinking distance + braking distance
What is thinking distance?
The distance traveled by a vehicle in the time it takes the driver to react to a stimulus
What is braking distance?
The distance traveled by the vehicle in the time between the brakes being applied and the vehicle actually stopping
What affects thinking distance?
- Tiredness
- Drugs
- Reaction time
- Speed at which the car is traveling
What affects braking distance?
- Poorly maintained roads
- Bad weather conditions
- The conditions of the car (e.g. worn brakes)
What is weight?
The force of gravity acting upon an object
What is the extension of a spring?
The difference between the length of the spring and its original length
What happens when an object falls through a fluid?
- Drag force is exerted on the object, resisting its motion
- The faster the object falls, the bigger the drag force becomes
- Eventually it will be equal to the weight of the object
- The resultant force on the object is now 0, so it stops accelerating
- It moves at a constant velocity so has reached its terminal velocity
What is an elastic object?
An object that regains its original shape when the forces deforming it are removed
What is the relationship between the extension of a spring/elastic object and the force applied to it?
They are directly proportional until the limit of proportionality is reached/exceeded
What is the limit of proportionality?
The limit of Hooke’s law applied to the extension of a spring
What is Hooke’s law?
The extension of an elastic object/spring is directly proportional to the force applied provided the limit of proportionality is not exceeded
What is the spring constant (k) measured in?
N/m
What happens to an elastic object/spring when the stretching force is removed?
The stored elastic potential energy is released as another type of energy
Complete the sentence:
The stiffer the spring…
…the greater its spring constant
What is fuel economy?
Reducing the amount of fuel a vehicle uses to travel a particular distance
Why does reducing air resistance improve fuel economy and how can this be done?
- By making a car more streamlined
- Means less energy and power is needed to maintain a certain speed
- Therefore less fuel is used
What causes skidding?
- When the brakes on a vehicle are applied too harshly
- When a vehicle skids, the wheels lock and slide along the road surface
- This increases stopping distance
What can be done to reduce skidding?
- Use anti-skid road surfaces
- These are rougher than normal surfaces
- This increases the friciton between tyres and the road
- They are used in places where drivers are likely to brake, such as near traffic lights and road junctions
What are speed cameras used for and how do they work?
- Used to discourage motorists from speeding
- Can determine the speed of a motorist at a particular point
- Can also be used in pairs to determine the speed at two points, and so can calculate an average speed
- Motorists going above the speed limit will be fined and may lose their licence
