Mechanics

1. Motion

   Annotations:

   • A scalar quantity has a size (or magnitude) but no particular direction. E.g. temperature, time, energy and power. A vector quantity has both magnitude and direction associated with it. Forces are vector quantities. A vector is drawn as a straight arrow line; the length of the line represents the magnitude of the vector, while the arrow points in the direction.
2. Forces

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   • Newton's first law says when the unbalanced (or resultant) force on an object is zero, the acceleration will also be zero. An object with zero acceleration will either be stationary or moving in a straight line at a steady speed Newton's second law says when an unbalanced force acts on an object it causes an acceleration. The acceleration a is directly proportional to the size of the force F, and inversely proportional to the mass m of the object.
3. Momentum

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   • All objects have momentum when they are moving. The greater the momentum, the more 'impact' the object will have if it hits something. Momentum is an especially useful quantity to use when studying collisions between objects, or explosions which force objects apart.
   1. Conservation of momentum

      Annotations:

      • In collisions or explosions, the total momentum of the objects involved is conserved. This happens provided there are no unbalanced external forces such as friction or gravity affecting the objects
   2. Centre of mass
4. Energy

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   • Energy is one of the most fundamental ideas in physics-it is the capacity to do work. There are many forms of energy-heat, light, sound, electrical, nuclear. All measured in joules
   1. Kinetic energy

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      • The energy an object has because its moving. An object of mass m and speed v has kinetic energy.
   2. GPE

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      • Is gained by an object when lifted vertically against the force of gravity.
   3. EPE

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      • is stored in a spring which is stretched or compressed. A spring (or force constant k) stretched (or compressed) by a distance y has elastic potential energy.
5. Impulse

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   • If the velocity of an object must have accelerated and so must have been acted on by an unbalanced force. A change in velocity means there must also be a change in momentum. The change in momentum is called the impulse of the force.

1. Centripetal acceleration and force

   Annotations:

   • An object moving in a circle is always changing its velocity and therefore must be accelerating. If its speed stays constant, then the change in velocity is caused only by a change in direction and the acceleration is called a centripetal acceleration. Acceleration is always caused by an unbalanced force acting in the same direction. The unbalanced force that causes a centripetal acceleration is called a centripetal force. A=v2/r  F=mv2/r
2. Gravitational force

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• Spinning motion around the centre of mass

1. Angular displacement

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   • Is measured in radians.
2. Angular velocity

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   • To describe how quickly an object is rotating, the angular velocity is used. Angular velocity has the symbol w, and is measured in units of radians per second.
3. Angular acceleration

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   • When the angular velocity of a object is changing, this is called angular acceleration.
4. Torque

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   • The turning effect of a force is called the torque. The size of the torque depends on the size of the force and the perpendicular distance from the force to the centre of rotation.
5. Rotational inertia

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   • Unbalanced torque causes angular acceleration. I gives a measure of how reluctant the object is to change its angular speed and is rotational inertia.
6. Angular momentum

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   • Any rotating object has angular momentum.
7. Rotational energy

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   • The energy an object has when spinning is called rotational kinetic energy.

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• In SHM the acceleration is proportional to the distance in the reverse direction.

1. Oscillatory motion

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   • Many kinds of motion are oscillating or periodic (repetitive motion). The 2 important quantities in describing any periodic motion are the frequency and period. Frequency is the number of times the motion repeats itself in one second. Measured in Hertz Period is the time taken for one complete cycle of the periodic motion. Measured in seconds. T=1/f and f=1/T
2. Phasors

   Annotations:

   • Is a rotating radius vector.
3. Displacement, velocity and acceleration
4. Mass on a spring

   Annotations:

   • The force F required to stretch a spring, is proportional to the extension or compression. y, of the spring from its natural length.