Lab E Ground Reaction Forces Introduction The ground reaction forces lab was utilized in order to investigate the differences and similarities between ground reaction forces between two different locomotions walking and running We were able to evaluate the contrast between running and walking kinematics and kinetics Ground reaction force which are vectors is the most common force acting on the body and we measure this using a force platform The force platform that we use in the lab utilizes a strain gauge platform The participant will step on the plate which deforms it and results in a change in the resistance of the strain gauge which changes the voltage of the bridge circuit and amplifies the voltage An A D converter is then used to give us the force trace that we see on the desktop computer In the lab we used a force plate that worked with PASCOairlink to record our horizontal and vertical directions with a sampling frequency of 100 Hz samples per second We collected data from a participant walking and running over a force plate at a steady speed with a normal gait pattern while striking the force pattern with her right foot This data can further also explore Newton s Third Law for every action there is an equal and opposite reaction because ground reaction forces are contact forces Methods Before we began the experiment we recorded the participants weight in Newtons using our force plate The 21 year old female was then asked to start the experiment by standing on the force plate and holding a steady position which gave us the Normal Force graph We were then able to complete four total trials two walking and two running Our group chose to complete four trials in order to verify the reliability of our data The female started about 5 yards from the force plate and she first walked over the force plate while having her right foot step on the force plate along the way with the cord on her right side This gave us a walking force trace on our desktop We repeated that step over again She then completed the same process but this time she ran over the force plate one foot stepping on the plate as she crossed This gave us a running force trace on our desktop and we once again repeated this running trial over again Results Gait Type Peak Vertical GRF BW Midtance Vertical GRF BW Range of Horizontal GRF BW Midtance Horizontal GRF BW Foot Contact Time BW Walking Running 1 033 2 023 0 781 2 009 0 282 0 334 0 000 0 001 0 690 0 360 Discussion When comparing the curve shapes for our walking and running graphs it is fairly apparent that the running graph comes to a thinner peak while the walking graph has a more gradual shape Therefore we can analyze that the running graph reaches a higher force in Newtons while the walking graph has a smaller force in Newtons This makes sense realistically because when we run our bodies become heavier and will hit the ground with a harder force than they would if we were walking We are also able to identify a similarity that both curves start at 0 newtons which makes sense because our participant is starting from standing The force plate that we use measures vertical normal force and horizontal parallel force and we can further relate that to the center of mass acceleration or even further Newton s Second Law In this case we need to consider body weight so we use the equation F ma BW BW referring to body weight When our participant is walking or running across the force plate we are in motion and our center of mass has some amount of acceleration Since we are using a force plate we also have to consider body weight so therefore the only variable changing in the equation is the acceleration The center of mass acceleration has a similar path as ground reaction force in regards to our lab Overall we can see the link between kinetics and kinematics through Newton s Second Law F ma Looking at the curves for walking graphs and running graphs when comparing the appearance of the horizontal ground force reactions we can see that the two curves appear very similar They both start at 0 Newtons and stay very close to the horizontal axis throughout the curve The walking graph only has the curve get to highest 600 Newtons while the running graph only sees the curve reach 32 Newtons at its highest The largest difference between the two curves is that the running curve hits a higher peak than the walking curve In regards to the center of mass and its relation to the measured ground reaction force we can first look at walking and the vertical ground reaction force There are many phases of the gait cycle and the most important one to look at when analyzing ground reaction force is midstance The center of mass velocity and the center of mass acceleration will allow us to see the size of the dip in the curve on the graph and further let us identify that the center of mass displacement is at a maximum and the the center of mass velocity is at 0 when the ground reaction force is at a minimum This tells us the center of mass is slowing down in the positive vertical direction which gives us the downward acceleration We can also look at the walking graph in regards to the anterior posterior ground reaction force Here we see that the dip at midstance in the vertical ground reaction force occurs at the same period that the anterior posterior graph is crossing zero in the positive direction In regards to the running gait cycle we see that at mid stance in running the center of mass position is at a minimum which is the opposite of the walking gait cycle The ground reaction force peak in running also occurs right at midstance in between braking and propulsion and the center of mass position is at a minimum at that position There is a greater force there as well and this is because the velocity is changing its direction negatively and the acceleration is going in a positive direction