Formulas for Kinematics
Category: Kinematics
Define acceleration due to free fall
Acceleration due to free fall refers to the acceleration of an object that is near to the Earth, free-falling towards the ground. This acceleration is constant and approximately 10 m/s2.
Define speed, velocity, acceleration, uniform acceleration
Speed is the change in distance per unit time.
Velocity is the change in displacement per unit time.
Acceleration is the change in velocity per unit time.
Uniform acceleration refers to a uniform change in velocity over time.
Ball falling off a cliff
A metal sphere, mass 2kg, and a wooden sphere, mass 1kg, of the same size, are dropped at the same time from the same height of 5m, on Earth. Which sphere would hit the ground first? Explain.
Both spheres would hit the ground at the same time.
The spheres are dropped near to ground, so the effect of air resistance on the spheres’ resultant force is negligible.
The resultant force acting on the sphere will be its downward weight.
The ratio of the weight to mass will be 10 for each sphere, so both spheres will free-fall towards the ground at a constant acceleration of 10m/s2.
Explain, in terms of forces, how a speed-time graph change.
Initially, the car’s speed is increasing. This causes the frictional forces to increase. With the forward driving force remaining constant, the resultant force acting on the car will be decreasing.
Since resultant force = mass x acceleration, with a decreasing resultant force, and constant mass, acceleration will be decreasing. This is represented by the decreasing gradient of the speed-time graph.
Eventually, the forward driving force will be equal to frictional forces. When this happens, resultant force acting on the car will be zero, so acceleration will be zero, and the car will be moving at constant speed. This is represented by the horizontal portion of the speed-time graph.