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Weight = the force on an object due to gravity
Weight(N) = Mass(Kg) x Gravity(ms-2)
measured in Newtons (N)
Relationship between gravitational potential energy and work done.
Gravitational Potential Energy of an object in a gravitational field is the work done in moving an object from an infinite distance to that point
Work = Fd = mgd = mgh
Practical: Acceleration due to gravity using a pendulum
Aim: to calculate the acceration due to gravity using a pendulum
Hypothesis: The calculation will be a ≈ 9.8ms-2
Risk: the weighted retort stand may be top heavy, causing it to fall off the desk and cause significant damage to those nearby. Therefore weight the retort stand down using a battery pack.
Materials: 1x retort stand, 1x protractor, 1x battery pack, 1x metal ball, 1x length of string, 1x scissors, 1x ruler, 1x mass balance, 1x stopwatch
Method: 1. measure the mass of the metal ball, m. 2. set up the simple pendulum with string length 1.2m. 3. measure an angle of 20° then release, timing t for 5 swings 4. repeat step 2 and 3 two more times keeping the angle and mass constant. 5. calculate average time and then period, T (time for one swing). 6. repeat steps 2-5 for Length, L, of range 0.2 to 1.2m 7. Graph T2 against L and use the gradient o determine the acceleration due to gravity.
Graph of T2 against L will result in a straight diagonal line. comment: accurate as T2 is directly proportional to L (from equation T2 = (4π2L)/g)
Results: Using values of T2 and equation T2 = (4π2L)/g) calculate a value for g.
Discussion: repetitions ensured reliability however a number of errors including the string's mass and air resistance not being taken into account. timing errors from reaction time and measurement errors associated with measuring the 20° angle.
Conclusion: Length was the variable effecting T. Equation varified at T recorded ≈ T estimated from equation. Acceleration measured to be 9.78 ms-2
universal gravitational constant
G = 6.67 x 10-7 N(m/kg)2
Newton's second law
Force (F) = Mass (m) x Gravity (a)
measured in Newtons (N)
Gravitational Potential Energy
GPE of an object at a point in a gravitational field = work done in moving the object from a infinite distance to that point.
Ep = -(Gm1m2)/r
Ep is highest at infinity when the object escapes the gravitational field (0J) and lowest at the surface of the object providing the field (negative)
When an object is lifted against a gravitational field work is done and Ep increases
As an object moves towards the source of the field Ep ⇒ Ek