Motion
Acceleration can be caused by…
…applying a force to an object, whether it be stationary or moving.
True or False? The line of gravity is an imaginary vertical line from the centre of gravity to the ground or surface the object or person is on.
True
Explain how flotation can occur.
Floatation is caused by a force known as buoyancy. In order for an object to float, the water they displace must weigh more than they do.
How does the body create force?
By manipulating the gravitational force on the body and by generating force using its muscles.
Provide the definition of linear motion and an example.
Linear motion is movement in a straight line. E.g. ball moving in a straight line/downhill skier holding a particular body position as they move in a straight line/swimmer when they glide off the wall.
Fill in the gaps: The ________ the line of gravity is to the centre of the base of support, the better balanced a person is in this position.
The closer the line of gravity is to the centre of the base of support (your next dash point) the better balanced a person is in this position.
Explain why it is easier the float in the ocean than in a pool?
For an object to have less gravitational force than the water it displaces it must be less dense (mass per unit of volume) than the water. Not all water has the same density though. Salt water is more dense than fresh water, and the saltier it is the larger the density.
Describe how the body absorbs force when catching a ball.
The force from the ball is absorbed by the body through eccentric contractions in the shoulders, trunk and arms. These contractions absorb the force over a longer period of time, making it easier to control and increasing the chances of the athlete holding onto the ball.
What is general motion.
Our body produces forces that cause angular motion of our joints that are then combined to cause linear motion of our bodies. E.g. the snowboarder.
What is the difference between balance and stability?
Balance is a person’s ability to control their equilibrium in relation to gravity only, whereas stability is your body’s ability to return to a desired position or trajectory following a disturbance to equilibrium.
What is an example of how athletes have used fluid resistance to benefit in sports that involve balls.
When kicking a free kick in football (soccer), the player kicks the ball to spin sidewards, therefore the ball will move in the direction of the spin on the ball.
How does one absorb force safely?
In order to absorb large forces safely, our body seeks to absorb the force by increasing the time of absorption, increasing the movement length used to absorb the force, or increasing the area in which the force is absorbed.
What is velocity and how is it different to speed?
Velocity is the displacement of an object over time and includes direction. Speed does not have direction attached to it, and is the distance covered by the athlete in a specified time.
Describe how lowering your centre of gravity can increase stability with the help of two sporting examples.
Lowering your centre of gravity helps to increase stability because it needs to be lifted higher before it moves outside of the base of support. This becomes very useful in combat sports such a jujitsu or sumo wrestling. It is also used by blockers in the NFL or to create a more effective rugby league tackle.
What is fluid resistance and how has clothing been adjusted in order to cause less friction (drag).
Fluid resistance refers to the forces a fluid places on a moving object in the opposite direction to the movement. The swim cap, goggles and swim suits that covered larger portions of the body, such as the full-length suit (that were banned from competition in 2010), contribute to the streamlined foil that created less pressure drag through the water.
How can the body apply force to the ball in a free kick in football (soccer)?
The body can help to generate force, by using gravity and momentum from movement and transferring the force into the object. This can be seen in a power shot in football, where the athlete will take a run up, to generate momentum. When they then plant their foot next to the ball before kicking it, they will bend the planted leg, drop their centre of gravity and then use the muscles in their torso and legs to generate the force of the kick.
How is momentum related to acceleration?
In order to accelerate, the force acts upon an object. The heavier the object the larger the force that is required to move it, and the motion will be slower than a lighter object that receives or produces the same force. So the lighter player can move faster and accelerate more quickly than the heavier player because the forward requires more force to reach the same velocity.
Describe the base of support in relation to a rugby player.
The larger the base of support the more stable the person/athlete is able to be. For example, the rugby player who is weaving through her opponents has a small base of support, to make her more agile, but she is also less stable.
Describe how principles of fluid mechanics have influenced modifications e.g. clothing/suits.
Some examples of modifications that have occurred to take advantage of buoyancy include the Speedo LZR Racer suit, which trapped air making the swimmer more buoyant, lifting them higher in the water so that they had less drag from the water and increased their speed, reducing their times in events.
Describe how an athlete would generate force to complete the vertical jump test.
Gravity and the lower body muscle contractions create a force in the downward direction into the ground. This force is then met by an equal and opposite reaction force that propels the athlete into the air. The greater the downward force the greater the reaction force, and the higher the athlete jumps. Further upward force is generated by the vertical acceleration of the arms to create a thrust in the vertical direction.