motion and forces

• The weight of an object is the gravitational pull on it by Earth's mass.
• Weight can be calculated as W = mg (Newton's second law).
• Gravity pulls objects towards the center of the earth with a constant acceleration of approximately 9.8 m/s2.
• Gravity pulls objects towards the center of the earth.
• Gravity causes objects with mass to have weight, which is the measure of the force exerted on them by gravity.
• Forces are measured using newtons (N) and have both magnitude and direction.
• Air resistance opposes motion through air and increases with speed.
• a scalar quantity has magnitude (size) only
• a vector quantity has both magnitude and direction
• Examples of scalars are distance, mass, speed, time, temperature, and energy.
• Examples of vectors are force, weight, velocity, acceleration, momentum, electric field strength and gravitational speed strength
• v=s/t (distance=speed/time)
• velocity is speed in a given direction
• average speed = total distance / total time taken (m/s)
• Calculating area under a speed time graph to find distance:

  • area of rectangle = width(height)
  • area of triangle = 1/2 base (height)
• acceleration of a free fall (g) near the earths surface = 9.8 m/s^2
• acceleration is the change in velocity per unit time
• a=v-u/ delta t
• acceleration = final velocity- initial velocity/ change in time
• deceleration is negative acceleration
• earths gravity is equally strong at all points close to earths surface
• all objects fall with the same acceleration PROVIDED that there is no air resistance
• terminal velocity is the greatest speed reached by an object when moving through a fluid
• gravitational field strength is the gravitational force exerted per unit mass placed at that point
• g=w/m (g=gravity, w=weight, m=mass)
• gravity is also = 9.8N/Kg
• weight is the effect of a gravitational field on a mass
• density is the mass per unit volume of a substance, measured in kg/m3
• p=m/v ( density=mass/volume)
• an object will float if the liquid it is submerged in is more dense than it
• forces may produce changes in the size and shape of an object
• a resultant force may change the velocity of an object by changing its direction of motion or its speed
• the spring constant is the force per unit extention of a spring, measured in newtons per metre
• k=f/x (spring constant= force/unit extension)
• earths gravity is equally strong at all points close to the earths surface
• mass is the measure of the quantity of matter in an object at rest relative to the observer
• weights is the gravitational force on an object that has mass
• g= w/m
• weight is the effect of a gravitational field on a mass
• density is the mass per unit volume