F = ma
Force (F) is the product of mass (m),acceleration (a). Force is recorded in Newtons (N), mass is measured in kilograms (kg), and acceleration, which is the change of an object's velocity over time, is measured in meters per second squared (m/s2).
however, when the direction of the force is on an angle we use …
F = ma(cosΘ)
Force (F) is the product of mass (m),acceleration (a), and the cosine of theta, or the angle between the direction of force and direction of displacement. The displacement is not the same as distance traveled, rather its the distance from its initial position to its final position; so while the weight’s motion during a bicep curl is technically a semicircle, we consider the displacement to be the straight vertical line between the starting and ending positions of the exercise. Just like when it’s a straight line, Force is recorded in Newtons (N), mass is measured in kilograms (kg), and acceleration, which is the change of an object's velocity over time, is measured in meters per second squared (m/s2).
I'm sure you thought you'd never have to use this stuff again after high school trigonometry, but unfortunately the angle at which the force is exerted is necessary for an accurate calculation. The cosine of any angle is a value between 0 and 1, here are some of the most common ones:
cosine(0°) = 1 |cosine(30°) = 0.866 |cosine(45°) = 0.707 |cosine(60°) = 0.5 |cosine(90°) = 0
When the force and the motion of the exercise are in the same direction,theta is 0°. Because the cosine(0°) = 1, it has no affect on the force calculation. But this is not always the case and we (unfortunately) have to use some trigonometry to account for these differences.
Another thing to consider are which units we're using - always remember to check and convert units!
1 kg = 2.2 lbs | 1 m = 3.28 ft
Work = Force x Displacement
Work is the product of the force exerted on an object and the distance the object moves in the direction of the force, while poweris the rate of doing work. Work and power are considered either "positive" or "negative" depending on the directions of force and displacement.If the force exerted by the muscle and the object's displacement are in the same direction, like during the lifting phase, then the work and power are considered to be positive.But if the force and displacement are in opposite directions, like during a controlled lowering phase, then the work and power are considered to be negative.
Although it should be stated that there is actually no such thing as negative work or power. It's just a way to refer to the work or power done ona muscle by the weight, like when the weight is going down during a bicep curl.When the weight is going up during a curl,the work is done onthe weight by the muscle and it is considered positive work or power.So while you're lifting and lowering a weight, your muscle and the weight are taking turns performing work on each other.Its not the muscle performing positive and negative work.We're just calculating everything relative to the muscle by saying that work or power done on it is negative.
