The new specification for AQA AS and A-level have been approved and are on the AQA website. The previous blog detailed some of the new content, and this one is going to work along the same lines, trying to be helpful by providing suitable notes / explanations of each (most) of this new content.
We looked at venous return and vitamins and minerals last time; today we’ll investigate stability and Vygotsky.
The term centre of mass is often used synonymously with centre of gravity and is the point of an object where its weight acts. If the object has a uniform shape and density, then the centre of mass is at the centre of the shape.
If a force is applied through the centre of mass of a body (a concentric force) the body will move in straight line. There is linear motion. However, if the applied force does not pass through the centre of mass (an eccentric force), this causes angular motion and the object will rotate when it moves. The rotation will be about the centre of mass.
Stability and Equilibrium
All objects at rest are in equilibrium. All the forces acting on them are balanced; the sum of all linear forces equals zero and the sum of all turning forces equals zero. If a force is applied to an object in equilibrium it will either tilt, tip over or roll.
These three conditions are known as:
• stable equilibrium (it tilts and then falls back to the original position)
• unstable equilibrium (it tilts and then falls over)
• neutral equilibrium (it rolls)
Stable equilibrium is the state where a body tends to return to its original position after being disturbed. Such as when an object such as a shoe box, is resting on its largest side and is lifted slightly and dropped. It will move back to its original position because it is in stable equilibrium.
Unstable equilibrium occurs where a body, if it is slightly displaced, it moves further away from its original position. Such as when an object (shoe box) is balancing on its shortest side and any slight movement causes it to become unstable and topple over.
Neutral equilibrium is when a body’s centre of mass is neither raised nor lowered, but stays at the same level when it is disturbed. For example when an object such as a ball on a level floor if moved, it maintains its neutral equilibrium
The ability to maintain balance under unfavorable circumstances is a basic motor skill and depends on the following factors:
• Size of the base of support.
• Relation of the line of gravity to the base of support.
• Height of the center of mass
• During movement – mass
The centre of mass must remain within the base of support to maintain equilibrium. Stability is easier with a larger base of support, because it becomes easier to keep the centre of mass within the base of support.
In gymnastics it is much easier to maintain balance during a headstand than a handstand because the headstand has a much larger base of support. Increasing the area of the base of support increases the stability of an object, the bigger the area the more stable the object. Rugby players will stand with their feet well apart if they are standing and expect to be tackled because the bigger base of support makes them more stable.
If an object is tilted it will topple over if a vertical line from its centre of mass (the line of gravity) falls outside its base of support. To maintain equilibrium, line of gravity must remain within the base of support.
The height of centre of mass in humans changes with body position. The closer the centre of mass to the base of support the more stable a performer becomes. Conversely the higher the centre of mass above the base of support the less stable the performer becomes. The rugby player, wrestler stays close to the ground to lower their centre of mass and increase their stability.
To help ourselves balance we can vary the position of our own centre of gravity by moving our arms and bodies to keep us from falling over.
When a body is moving, or an external force is being applied to a body, then the greater the mass the greater the stability. The greater the mass, the more force is needed to affect its stability by overcoming its inertia.
Vygotsky and Constructivism
To construct means to build, and that is what this theory suggests, you build on what you know! Working with others helps to develop skills because you can learn from the actions of those who are more experienced and add their actions to the ones you already know. By interacting with others and copying their actions, skills can be improved. This process is called socialisation.
Vygotsky suggested that learning is developed through three stages, based on what you need to learn next:
1. Can do alone
2. Can do with help
3. Cannot yet do
In a sport such as hockey, the performer will build up their learning through each stage. So initially they may be able to hold the stick and use it to roll the ball along the ground; they can do this by themselves. They may however not be able to keep the ball close to the stick when running with it without the help of the coach or other players and they can’t yet do a complete dribble with the ball in practice against other players.
To help them learn this skill they need to observe and copy others and take advice. Learning and copying from others is called social learning. The actual actions that are needed to take the performer to the next stage are up to the performer and will be decided based on the performer’s experience and expectations. The people with more experience and skills that the performer learns from are called More Knowledgeable Others by Vygotsky.
Vygotsky further suggested that learning is based on the ‘Zone of Proximal Development’. Proximal simply means what you need to do next, so the performer uses their experience to take note of their current level of performance and decides what to learn next. Vygotsky also suggested that learning is best done when others are present, so that as in our example, the hockey dribble is best learned with the help of people like the hockey coach and team mates.
Hope this helps some people. We’ll cover more – The key data terms qualitative and quantitative; Definitions, equations and units of example scalars; Understanding the impact of physical activity and sport on the health and fitness of the individual; Impact of poor lifestyle choices on the respiratory system and The health, fitness and social benefits of raising participation in the next blog.