Lecture 15 - Linear Kinetics - Reaction Forces Flashcards
What is the net force?
The force you have acting on you after adding up all the forces acting on a body
What does the net force determine?
If there is an acceleration and in what direction
What causes an acceleration on the system?
A net force
What is the effective force?
The net sum of all force vectors acting on a body
How can you keep tract of all the forces on a system?
By drawing a free body diagram
How do you draw a free body diagram?
Draw the system isolated from the environment
Label the positive axes of your reference system
Identify the center of mass
Draw and label all the external forces acting on the system
What is a contact force?
The force created when two bodies are touching each other
What is a reaction force?
A force of equal magnitude and opposite direction created on an opposing body
What is a ground reaction force?
The equal and opposite force the ground applies back on a person
How can you determine the vertical effective force (vertical ground force)?
By subtracting the force from gravity (weight) from the ground direction force
What occurs if the ground reaction force is greater than the force of gravity
The body center of mass will accelerate upward
What occurs if the ground reaction force equals the force from gravity?
Then there will be no acceleration in the y direction.
What is the always true of the vertical ground reaction force?
It it always positive or equal to zero
What is the horizontal ground reaction force?
The force of friction between the ground and the shoe preventing slipping in the x direction
What study did Ashby and Heegaard conduct in 2002?
“Role of Arm Motion in the Standing Long Jump” - Journal of Biomechanics
What did Ashby and Heegaard investigate in their study?
The role of arm motion on the performance of a standing long jump
How many subjects did Ashby and Heegaard use in their study?
3 males
What types of jumps did Ashby and Heegaard use in their study?
Jumps with free arm motion and jumps with restricted arm motion
What question did Ashby and Heegaard test in their study?
Does arm swing improve jumping distance?
What had previous studies shown about standing vertical jumps?
Arm swing improves jump height by:
Increasing the height and velocity of the body’s center of gravity at take off
Contributing to the total body vertical momentum
Increasing the peak magnitude of the vertical ground reaction force
What had previous studies shown about the downward force of arm swings?
Arm swing may create additional downward forces on the body that slows the contraction of hip and knee extensors, enabling greater muscle force development
What have previous studies shown to be the reason why maintaining balance is more difficult during a standing long jump?
Because the center of gravity does not remain over the lower body throughout the motion
What was Ashby and Heegaard’s hypothesis?
Standing long jump performance is improved when arm movements is employed in the standing long jump
What kinds of subjects were used in Ashby and Heegaard’s study?
Untrained males
