physics (newtons laws)

• Balanced and unbalanced force

  Balanced forces are forces that are equal in magnitude (size) but opposite in direction.

  Balanced forces have the same effect as no force at all. When the forces on an object are balanced (or when there are no forces at all), then neither the speed nor direction of movement will change.

  When several forces act on one object, they can be replaced by one force which has the same effect. This single force is called the resultant or unbalanced force.

  Forces acting in the same direction can be added together.
• newtons first law and unbalanced/balanced forces

  "A body will remain at rest or travel at constant velocity, unless acted upon by an unbalanced force".

  What this means is that:

  Balanced forces result in:

  • remaining at rest
  • constant speed

  Unbalanced forces result in:

  • acceleration
  • deceleration

  Remember

  Acceleration is the change in velocity per second.

  Since velocity as a vector has a magnitude and direction, an object travelling at a constant speed but changing direction is also accelerating.
• Solve problems involving unbalanced force, mass and acceleration

  An object that with an unbalanced force acting upon it will accelerate. The acceleration is directly proportional to the magnitude of the unbalanced force, meaning the greater the unbalanced force the greater the acceleration in the direction of the unbalanced force.

  Acceleration is inversely proportional to the mass of the object meaning the greater the mass the less the acceleration for the same unbalanced force.
• Solve problems involving weight, mass and gravitational field strength

  Mass is a measure of the amount of matter (stuff) in an object. It is measured in kilograms (kg). Weight is a force and it is downwards force acting on the object due to gravity. It is measured in Newtons.

  Gravitational field strength, g, is measured in Newtons per kilogram. It is the weight per unit mass (force of gravity on every kilogram). On Earth the gravitational field strength has a value of 9.8 Nkg-1.
• Explain motion resulting from a ‘reaction’ force in terms of Newton’s third law

  Newton’s Third Law states:

  For every action there is an equal but opposite reaction.

  or

  If A exerts a force on B, B exerts an equal and opposite force on A.

  for example, a footballer heading a ball.Object A is the head. Object B is the ball. When the player heads the ball, the head exerts a force to the right on the ball. The ball exerts a force on the head that is equal in size and opposite in direction.