Week 6-9 Flashcards
Describe the two types of forces
Internal forces- sum to zero and can’t accelerate body (muscles and ligaments)
External forces - dont have to sum to zero and can accelerate body (contact between two bodies)
What are the two types of external forces
Gravity - 9.81m/s
Contact forces - can accelerate you any amount
How do you measure ground reaction forces?
Force plate or insoles
What are the 3 components of ground reaction forces?
Perpendicular to surface - normal force Fz
Parallel to surface - Fx and Fy, friction forces
Describe the factors that affect friction
Surface area - friction doesn’t depend on surface area
Contact surface - softer, rougher surfaces have greater friction and harder, smoother surfaces have less friction
What is stability related to?
Related to the distance from the centre of pressure to the base of support
To stop motion you need to decrease momentum, how do you do this?
Increase force (difficult) or increase time
What are elastic collisions?
No external forces and kinetic energy stays constant, bodies bounce off eachother
What are inelastic collisions?
The two bodies stick together
What is the coefficient of restitution
measure of how elastic a collision is (or how much energy is returned). In perfect elastic collisions the coefficient of restitution is 1. In perfect inelastic collisions the coefficient is 0.
What is torque
Turning effect of a force, it is a vector
When does static equilibrium exist?
when force and torque equals zero.
What is the moment of inertia?
The torque needed to for a desired angular acceleration around a rotational axis
What is angular momentum?
Quantity of rotation of a body, found by inertia x angular velocity. A closed system
What are the 4 main sources of energy?
Chemical, electrical, heat and mechanical
