Inertia & Mass
Define inertia and state the variable that causes inertia to change.
The tendency of a body or object to maintain either a resting state or a state of constant velocity.
Variable = mass.
State the equation used to determine force
F=MA (measured in Newtons - N)
Define momentum and state the equation
The amount of motion an object has and its resistance to change. P=MV
Define impulse
The change in momentum of an object, due to a small/large force being applied for a long/short time to increase or decrease an objects velocity.
State 3-4 factors that affect the stability, balance and equilibrium of an object
COG, LOG, BOS, Friction
Define moment of inertia
The tendency of an object to maintain constant angular velocity (ie. resistance to change). It is determined by the distribution of an object's mass about the axis of rotation.
Name two types of external forces that can act on a body to either accelerate, slow down or change direction of an object/body.
Gravity (9.8m/s2)
Drag (air and water resistance)
Weight (mass x gravity)
Friction
angular velocity x moment of inertia
What are the two goals of manipulating momentum?
Maximise momentum (increase velocity)
Minimise momentum (decrease velocity)
Provide two tips to reduce stability and balance in order to promote agility.
Two of:
•Raising an object’s COG
•Shifting the line of gravity outside the base of support
•Narrowing the base of support
•Decreasing the friction between two or more bodies
•Decreasing the mass of an object
Provide a sporting example of Newton's First Law of Inertia
Definition: an object will remain in its current state of motion unless acted upon by an external force.
Bike collision, basketball being caught/thrown....
Define torque and state two factors that determine the amount of torque.
Torque is defined as a force that produces rotation. The amount of torque depends on:
- Size of the force
- Length of the lever
State 3 of the 5 principles of summation of momentum
activating the stronger and larger muscles first
using as many body parts as possible, enabling force to be generated over a greater time
transferring momentum from one body part to another when at maximum velocity.
the presence of a stable base for maximal acceleration of body parts to occur so that momentum can be transferred successfully from one body part to another
ensuring appropriate follow-through is used to prevent unnecessary deceleration of body parts
With reference to impulse, explain the concept of having "soft hands" when attempting to catch a ball in cricket.
By using soft hands the cricketer has increased the time it takes to change the momentum of the ball. This reduces the force impact of the ball as it hits the hands gradually reducing velocity making it easier to control and catch.
Provide 3 tips to increase stability and balance
•Lowering an object’s COG
•Ensuring the LOG is over the BOS
•Increasing the size of the BOS
•Increasing the friction between two or more bodies
•Increasing the mass of an object
•Extending the base of support in the direction from which a force is coming
Provide an example of static and dynamic inertia.
Static = the reluctance of a heavy piece of sports equipment to be moved, such as a barbell with weights on it.
Dynamic = the reluctance of a rugby player running quickly with the ball to be stopped (change of direction and velocity).
Arm wrestle application:
1.What is acting as the unbalanced force to change your arm’s state of motion?
2. For one game, you are going to give someone a head start, use your knowledge of force to suggest why this gives them a better chance of winning?
1. Your opponent's arm/force behind their arm
2. F=MA. As your opponent already has greater acceleration behind their arm, it will be more difficult for you to oppose their total force and overcome their current state of motion.
When a figure skater brings her arms in to her body and crossed them over, what is she trying to do?
Show your knowledge of impulse by explaining why a gymnast would land with bent knees when landing a dismount from a beam.
This is about breaking momentum. By landing with bent knees as opposed to stiff knees, the gymnast is able to decrease the force exerted through the knee joint by increasing the time over which that force is applied. Thereby absorbing more of the force over a longer period of time.
A sumo wrestler is standing their ground in anticipation of an incoming force (opposing wrestler). What should they do to their COG to assist them to maintain stability, balance and equilibrium?
Place their COG closer to the side of BOS that is expected to receive the force, ie. leaning into the opposing wrestler.
With reference to inertia, mass and Newton's 1st Law, explain how a sumo wrestler is able to push another wrestler out of the ring.
The sumo wrestler will remain in its current state of motion unless acted upon by an external force (rival sumo wrestler). Due to the increased mass of one of the wrestler's, they are able to overcome their opponent's reluctance to change their motion, and push them out of the ring.
Arm wrestle application:
1.Suppose 2 students are arm wrestling and neither can bring the other arm down. What can you infer about the forces being exerted?
2.What impact does putting some water on the desks have on the arm wrestle?
1. Net forces are equal
2. Reduces friction, make their contact point (elbow) with the desk less stable. This will reduce total force.
Explain how a diver in a tucked position mid-dive has the same angular momentum when just about to enter the water at full stretch.
Angular momentum = MOI x angular velocity. When tucked, MOI is reduced as more mass is distributed closer to the axis of rotation and angular velocity increases. When at full stretch, MOI increases as more mass is distributed away from the centre of axis, resulting in a decrease in angular velocity.
Explain why a shot putter completes a number of spins prior to projecting the shot put?
Circular movements when throwing a shot put helps to increase impulse. Hence, a greater force can be applied over an increased time of about 1-2 seconds. This will increase distance thrown when compared to releasing the shot put from a standstill.
A sumo wrestler is standing their ground in anticipation of an incoming force (opposing wrestler). What should they do to their BOS to assist them to maintain stability, balance and equilibrium?
Increase the base (feet width) in direction of expected force.