#Acceleration physics plus

Whether the free-fall acceleration is -9.8 m/s/s or +9.8 m/s/s depends on if you chose downward to be the negative or positive direction. We have just shown that in the absence of air resistance, all objects falling near the surface of Earth will experience an acceleration equal in size to 9.8 m/s 2, regardless of their mass and weight. We also see that the size, or magnitude, of the acceleration is g = 9.8 m/s 2. We see that our acceleration is negative, which makes sense because the acceleration is downward. Gravity is the net force in this case because it is the only force, so we just use the formula for calculating force of gravity near the surface of Earth, add a negative sign because down is our negative direction ( ), and enter that for the net force: : The net force is then just gravity, because it is the only force, so they are in free-fall for this moment. At this moment they have the force of gravity pulling them down, but they have not yet gained any speed, so the air resistance ( drag force) is zero. Let’s calculate the initial acceleration of our example skydiver the moment they jump. Acceleration calculation is essential for solving many problems in Physics. That force is actually more than three times greater than their body weight, but is distributed over the wide straps that make up the leg loops and waist loop of the harness, which helps to prevent injury. Acceleration is the rate of change of velocity of a moving body with time. The skydiver’s body weight is F g = 85 kg x 9.8 m/s/s = 833 N, so the force on them from the harness must be 2833 N.

#Acceleration physics plus

Therefore, the harness needs to support body weight plus provide the additional unbalanced 2200 N upward force on the person. When the chute begins to open the body position changes to feet first, which significantly reduces air resistance, so air resistance is no longer balancing the body weight. The person experiences an average net force of 2200 N upward during chute opening.

We start with Newton’s Second Law of Motion If the mass of our example skydiver is 85 kg, what is the average net force on the person? In the previous chapter we found that if opening a parachute slows a skydiver from 54 m/s to 2.7 m/s in just 2.0 s of time then they experienced an average upward acceleration of 26 m/s/s.