Download Calculating the Acceleration Due to Gravity and Impact Forces and more Study notes Mechanics in PDF only on Docsity!
Acceleration due to Gravity
Key Stage 4
Topics covered: force, mass, acceleration, gravitational field strength, impact forces.
Watch the video “Newton’s Laws of Motion”, https://vimeo.com/
Your weight is a force, F (N), caused by the effect of gravity. It depends on your mass, m (kg), but also on the acceleration, a (m/s^2 ), due to the gravity of the object that is pulling you towards it.
We can estimate the acceleration due to the gravity on the surface of the Earth using mechanics. If we ignore the effects of atmospheric drag and measure the time, t (s), for an object to fall from a height, d (m), then the acceleration due to the Earth’s gravity can be calculated using the equation below:
𝑡^2
Activity 1 - Calculating the acceleration due to gravity on Earth
Equipment : marble, 2 metre rulers + blue-tack, balance and stop clock
a) Measure the mass of the marble using the balance and record the result. Mass = ___________ kg
b) Stick the rulers vertically against a flat wall with one touching the ground and the other directly above it.
c) Choose 5 different heights to drop your marble from and time how long it takes to reach the ground. Fill in the table below as you collect your results. You may want to repeat and average your results if you have time.
Height, d (m) Time, t (s) 2d (m) t^2 (s^2 )
d) Plot a graph of 2d against t^2 and draw a line of best fit through your results.
e) Calculate the gradient of this line (equation 2) which will give you the acceleration due to the gravity of the Earth at its surface.
Calculated acceleration due to gravity _________________ units: _______
Extension
Because the Earth is not a perfect sphere (it bulges out more at the equator), the acceleration due to gravity is slightly less at the equator compared to the poles. Find your latitude by visiting: http://www.sensorsone.com/local- gravity-calculator/#latitude to see how close your calculated value is to your local acceleration due to gravity.
Size of parachute Time t, (s) Impact force F, (N) No parachute 20 cm x 20 cm 3 0 cm x 3 0 cm 4 0 cm x 4 0 cm 5 0 cm x 5 0 cm
- Why is it important that parachutes are used during the descent of landing space probes?
- How else could the landing force of a probe be reduced? (Watch the “Newton’s Laws of Motion” video for ideas)!
- What other factors might scientists think about when designing a parachute to help land a space probe safely on another planet or moon?
Acceleration due to Gravity: ANSWERS
Key Stage 4
Activity 1
Acceleration due to gravity: 9.8 (or close to this value) Units: kg m/s^2
Activity 2
𝑡^2
- Parachutes increase the time taken to fall and so help reduce the impact force experienced by a space probe. The larger the parachute, the smaller the impact force and so the lower the risk of damage to the probe.
- Small thrusters can be used as the probe gets close to the surface. They exert a downwards force which by Newton’s third law results in an upward force and this acts to help decelerate the falling probe.
Air bags around the probe (must withstand puncture from rocks).
- This list is not exhaustive: Material – resistance to heat, chemical resistance, weight, strength (needs to withstand great deceleration), permeability (whether it’s tightly woven or not i.e. more holes) Cost of manufacture and launch (extra load) Shape (and area) Length of shroud/ rigging lines / how they detach Does the planet have an atmosphere to provide atmospheric drag / help slow down the probe? Surface the probe will be landing on - is the terrain soft, hilly or does it have a liquid surface?
