Physics forces paper 2

• What is newtons 1st law?

  Unless acted on by a resultant force, an object will remain at rest or moving at a constant speed
• What is newtons 2nd law?

  Force = mass x acceleration

  (larger force = more acceleration)

  (larger mass = less acceleration)
• What is newtons 3rd law?

  Every action has an equal and opposite reaction
• Is force a vector or a scalar?

  A vector
• What is weight?

  A force on an object due to gravity, measure in newtons
• What is mass?

  The amount of matter in an object, measured in kg
• What is gravitational field strength?

  the weight of 1kg of an object, measured in N/kg
• Air resistance

  • Always opposes movement
  • the faster the object moves, the stronger the air resistance
• What is terminal velocity?

  when a object moves at a constant velocity
• What happens to an object as it falls?

  • At first, the only force acting on the object is its weight. This is unbalanced (has a resultant force) which makes it accelerate
  • as the object falls, its speed increases which means that the air resistance also increases.
  • eventually the force Of the air Resistance and weight become equal and balance (No resultant force). So the object stops accelerating and travels at a constant speed. This speed is called its terminal velocity
• What is the equation that link gravitational field strength, mass and weight?

  Weight = mass x gravitational field strength
• What is the gravitational field strength on earth?

  9.8 N/kg (planets with more mass will have stronger gravity)
• What is thinking time?

  The time taken for a driver to react to a hazard, and apply the breaks
• What is thinking distance?

  The distance travelled while the driver is reacting
• What is the braking distance?

  The distance travelled after the driver has reacted, and the brakes are applied
• What is stopping distance?

  The total distance required to stop from a given speed. The sum of the thinking and braking distances
• What are factors that affect stopping distance?

  1. Alcohol, drugs and tiredness increase the thinking distance
  2. a higher initial speed will increase the thinking and braking distances
  3. Wet or icy conditions will increase the braking distance
  4. poorly maintained tyres and brakes will increase the braking distance
• How do you calculate the stopping distance?

  thinking distance + braking distance
• Is momentum a vector or scalar?

  Vector
• Momentum

  • All moving objects have momentum
  • momentum is always conserved
  • momentum can be transferred between objects through collisions
• what will happen to an objects velocity when it hits another object at rest?

  The objects momentum will be transferred to the other object so it will lose velocity
• What does it mean if two objects coalesce?

  They join together and act as one object
• Impact forces

  • A change in momentum requires an external force
  • The faster the change of momentum, the larger the force
• What will happen to the impact force of an object if it slows down?

  it will become negative
• What do cars contain for safety?

  • Crumple zones
  • Seat belts
  • Air bags
• What does the crumple zone do?

  • Increases the time it takes for the car to stop
  • This reduces the size of the force exerted on the passengers, reducing the chance of injuries
• What do airbags do?

  • inflate on impact so that the heads movement is brought to rest over a longer time, reducing the size of the force on the head
• How can you reduce the pressure on a surface?

  By spreading a force out over a larger area
• Pressure in a fluid

  • Any object in a fluid will be under some pressure because of gravity acting on the fluid directly above the object
  • Deeper fluid = more pressure
  • Denser fluid = more pressure
  • Stronger gravity = more pressure
• The atmosphere

  • The atmosphere is a thin layer of air around the air
  • The air molecules collide with surfaces, exerting pressure
  • If an area of low pressure is created, the air will exert a force
• The atmosphere at altitude

  As you move up through the atmosphere:

  • There is less and less air above you
  • The air that is above you is less dense
  • Atmospheric pressure decreases with increasing altitude