Chapter 10 Force And Motion Flashcards
10.1 Resultant force equation
Mass x acceleration
10.1 What is inertia?
It changes the velocity of an object. The tendency of an object to stay at rest or to continue in uniform motion.
10.1 What happens to the resultant force if the velocity of an object is increasing?
The resultant force is at the same direction as the velocity.
10.1 What happens to the resultant force if the object’s velocity is decreasing?
The resultant force is the opposite direction to its velocity.
10.1 Newton’s second law of motion
The acceleration of an object is inversly proportional to the mass of an object.
10.6 How does the impact time reduce the impact force?
The longer the impact time, the more the impact force is reduced.
10.6 Impact force equation
Mass x change of velocity/ time taken
10.4 Momentum equation
Momentum = mass x velocity
10.4 What happens in a closed system in momentum?
In a closed system, the total momentum before an event is equal to the total momentum after the event.
10.5 Conservation of momentum equation
(mass of A x velocity A) + (mass of B x mass of velocity B) = 0
10.8 Force applied in a spring equation
Force applied = Spring constant x extension
10.2 What is the weight of an object?
The force acting on an object due to gravity
10.2 What is the mass of an object?
It depends on the quantity of matter in an object.
10.2 What is the equation of weight
Mass x gravitational field strength
10.2 What is the terminal velocity of an object?
The velocity it eventually reaches when it is falling. The weight of the object is then equal to the frictional force on the object.
10.2 How does an object reach terminal velocity?
- The acceleration of the object decreases as it falls. This is because the frictional force increases as it speeds up. So the resultant force on it decreases and therefore its acceleration decreases
- The object reaches a constant velocity when the frictional force on it is eqaul and opposite to its weight. This velocity is called its terminal velocity. The resultant force is then zero, so its acceleration is zero.
10.3 What does the braking force depend on?
- The speed of the vehicle when the brakes are first applied.
- The mass of the vehicle
10.3 What happens to the decelaration when the speed increases?
The greater the speed, the greater the deceleration
10.3 The greater the mass, what happens to the braking force?
The greater the mass, the greater the braking force
10.3 What is the thinking distance?
The distance travelled by the vehicle in the time it takes the driver to react. Formula is speed x reaction time.
10.3 What is the braking distance?
The distance travelled by the vehicle during the time the braking force acts.
10.3 What factors affect the braking distance?
High speed
Poor weather conditions
Poor vehicle maintenance
10.4 What factors increase the thinking distance
Tiredness
Alcohol
Drugs
Use of a mobile phone
10.4 What happens to the momentum in a closed system
The total momentum before an event is equal to the total momentum after the event. You can use this in calculations when objects collide
10.5 What is the formula of the conservation of momentum?
- (Mass of A x velocity of A) + (mass of B x velocity of B) =0
So…
2. (Mass of A x velocity of A) = - (Mass of B x velocity B)
10.5 In momentum, what happens when two objects push each other apart?
They move with different speeds if they have unequal masses, and with equal and opposite momentum, so their total momentum is zero.
10.5 What happens when MaVa + MbVb =0
The two objects (A and B) recoil from each other.
10.6 What happens when two vehicles collide
- They exert equal and opposite forces on each other.
- Their total momentum is unchanged.
10.6 Explain the impact force equation
- Impact force = change of momentum / impact time
- So the shorter the impact time, the greater the impact force.
10.6 How does a soft pad in front of a trolley reduce the impact force?
- A soft pad on the front of the trolley acts as a cushion to increase the impact time.
- The momentum of the trolley would be reduced over a longer time, and so the change of momentum per second would be less.
- Impact force is equal to the change of momentum per second, the impact force would be less.
10.7 Why are cycle helmets and cushioned surfaces used?
These reduce imoact forces by increasing the impact time.
10.7 Why are seat belts and air bags used?
They spread the force across the chest and increase the impact time.
10.7 Why are side impact bars and crumple zones used?
They give way in an impact, and so increase the impact time.
10.7 How can the conservation of momentum be used?
They can be used to find the speed of a car before an impact.
10.8 What does it mean when an object is elastic?
An object is elastic if it returns to its original shape after removing the force deforming it.
10.8 What is the extension of an object
The difference between the length of the object and its original length.
Extension = Length at the stage - original strength
10.8 What is the relationship between the extension and force applied?
The extension of a spring is directly proportional to the force applied to it, as long as the limit of proportionality is not exceeded. This relationship is linear.
10.8 What happens beyond the limit of proportionality?
The extension of a spring is no longer proportional to the applied force. This relationship becomes non-linear.
