Lesson - 1.2.6
Objects fall to the ground because they have weight. Their weight is caused by the gravitational field of the Earth, pulling downwards on their mass.
The Earth’s gravity is equally strong at all points close to the Earth’s surface. If you climb to the top of a tall building, your weight will stay the same. We say that there is a uniform gravitational field close to the Earth’s surface. As it does not matter if its a ball or a car , every objects have the same acceleration
Air resistance increases with the speed of motion. As the parachutist falls faster, eventually air resistance balances his weight. Then the parachutist stops accelerating: he falls at a steady rate known as the terminal velocity.
Free-fall parachutists, before they open their parachutes. They can reach a terminal velocity of more than 50 m/s. b: The forces on a falling parachutist. Notice that his weight is constant. When air resistance equals weight, the forces are balanced and the parachutist reaches a steady speed. The parachutist is always falling (velocity downwards), although his acceleration is upwards when he opens his parachute. c: A speed–time graph for a falling parachutist.
Going Round In Circle
By moving in a circle, an object will be changing direction continuously (all the time). Therefore, even if the object is moving at a constant speed, its velocity is changing. Remember that velocity is a vector and so has direction as well as magnitude (size).
If the velocity of an object is changing, it must be accelerating. This means that an unbalanced force is acting on the object and this force acts towards the centre of the circle. The resultant force that acts towards the centre of a circle is the result of a force acting perpendicular to the motion of the object.
The ‘wall of death’ is a stunt where motorcycles or cars appear to defy gravity as they are driven around the circular wall inside a giant cylinder . The vehicles do not slide down the wall because their weight is balanced by friction. As they move faster, the force of friction increases because the force pushing the vehicle towards the centre of the cylinder increases. If they were to stop, the vehicles would slide down the wall.