PHYSICS- Force and Motion

• What is acceleration


  Acceleration is the rate at which an object speeds up
• What is deceleration?


  Deceleration is the rate at which an object slows down.
• What is the unit for acceleration

  The unit for acceleration is m/s/s (metres per second per second)
• What does an acceleration of 1 m/s/s mean?


  An acceleration of 1 m/s/s tells us that every second an object's speed increases by 1 m/s
• What does a speed time graph tell us?

  A straight line tells us that the object is moving with constant acceleration. The steeper the line on a speed time graph the larger the object's acceleration. A flat line on a speed-time graph tells us the object is moving at a constant speed.
• What happens to an object when a resultant force acts on it in the direction its moving

  When a resultant force acts on an object in the direction it is moving that object accelerates and its kinetic store increases.
• What is the relationship between the size of an object's acceleration and the resultant force acting on it?

  the larger the resultant force acting on an object the larger that object's acceleration. Acceleration is directly proportional to resultant force. This means that if resultant force doubles acceleration doubles.
• What does a graph of acceleration against resultant force look like?

  A graph of acceleration against resultant force will be a straight line through the origin
• What happens to an object when a resultant force acts on it in the opposite direction to its motion?

  When a resultant force acts on an object in the opposite direction to motion that object will decelerate, its kinetic store will decrease and the thermal store of the surroundings will increase.
• When you push an object, and then let go, why does it slow down?

  The force you used to push the object is a contact force so as soon as the object is out of your hands there is no longer any contact and therefore no push force. In the absence of friction this object would keep on moving at a steady speed because there would be no resultant force on it. In reality the object will slow down because there is a resultant force acting on it the opposite direction to its motion; this is caused by friction between the object and the surface it is on.
• How do we stop moving vehicles?

  When we stop objects such as cars, we use the brakes to apply a force on the vehicle in the opposite direction to its motion.
• Why do we stop moving vehicles over a longer period of time?

  We try to apply the braking force over a longer period of time because this means the speed is reduced more slowly and this results in a smaller deceleration. Smaller decelerations require smaller esultant forces.
• Why do objects moving through air experience air resistance?

  When objects move through air there is air resistance forces that act on them because the object collides with air molecules.
• Why do larger surface areas and faster speeds result in more air resistance?

  The larger the surface area of the object and the faster it is moving the more air molecules it will collide with per second and the larger the air resistance force it will experience.
• What is terminal velocity?

  A falling object will accelerate to start with but then reaches a steady speed that we know as terminal velocity.
• What happens to an object dropped from a height initially?

  It accelerates downwards due to weight.
• Why does an object not accelerate forever when dropped?

  Air resistance increases, reducing resultant force.
• What happens to the acceleration of a falling object as it speeds up?

  It becomes smaller due to increased air resistance.
• What occurs when air resistance equals the weight of a falling object?

  There is no resultant force, and acceleration stops.
• What is the steady speed reached by a falling object called?

  Terminal velocity
• What are the key factors that determine terminal velocity for a falling object?

  • Weight of the object
  • Air resistance acting on the object
  • Shape and surface area of the object
  • Density of the fluid (air) through which it falls
• What energy transfers take place in an object falling at terminal velocity?

  An object falling at terminal velocity is losing height so its gravitational store is decreasing however because it is not getting any faster its kinetic store doesn't change. The energy lost from its gravitational store is transferred to the thermal store of the surroundings due to the work done by air resistance.
• What is acceleration?


  Acceleration is the rate at which an object speeds up.
• What is deceleration


  Deceleration is the rate at which an object slows down.