Let’s assume the stone is moving to the right. We will learn more about this later in the activity.ī) A curling stone, gliding forward along an ice surface. Since the bird is at rest, there is no acceleration, so those two forces must be equal. If the normal force was stronger than the gravitational force, the bird would accelerate upward. How did we know the normal force and the gravitational force would be the same magnitude? Think back to the bird on the branch - is it moving? If the gravitational force was stronger than the normal force, the bird would accelerate downward, breaking the branch. The longer the arrow (relative to the other arrows), the stronger the force. In the case of the bird, the normal force of the branch on the bird is exactly the same magnitude of the force of gravity on the bird, causing the bird to remain motionless on the branch. We represent this by drawing the arrows the same length. It would be incorrect to have drawn the following:Īlso, notice the sizes of the arrows. We are really only interested in the forces on the bird in this diagram, not what kind of bird is sitting on the branch!Įach of the forces acting on the bird are represented and labelled by arrows starting at the object and moving outward. “Hey - that bird looks a lot like a box!” In physics, we often represent objects as a box or a circle in free-body diagrams to keep things simple. A bird, standing motionless on a branch.Always acts in the direction parallel to the rope.Ĭan you identify the forces acting on each of the following objects?.Exists when an object is being pulled by a string, rope, chain, etc.Always acts in the opposite direction of an object’s motion.Exists when a moving object comes into contact with air (think friction, but due to the air instead of a surface).Typically acts in the opposite direction of an object’s motion (it is what slows down a skateboarder gliding down the street), or opposite an applied force on a stationary object (it is what keeps a heavy filing cabinet in place even when you are pushing on it).Exists when two objects are in contact with each other.For example, a person pushing on a car would have an applied force of. The direction of the force will depend on the situation.Įach applied force will have a different notation depending on the source of the force.Exists when two objects interact with each other.Always acts in the direction perpendicular to the surface upon which the object is resting.Exists when an object is in contact with a surface (like a book sitting on a table, or a skater gliding on the ice, or a box on a ramp), usually to counteract the force of gravity.Known as an action-at-a-distance force: two objects do not need to be in contact with each other in order to experience a gravitational force.Always acts on the object in the direction.Exists between a planet (usually the Earth) or other large body and the object in question dependant on the object’s mass.
To simplify, each force is defined separately, however there is almost always a combination of forces acting on any given object. Throughout this activity, we will look at six types of forces that impact us every day.
The symbol for force is, and forces are measured in newtons - the reason for this will become apparent later in this activity! Don’t forget, that objects don’t necessarily need to be touching in order to interact, for instance the Earth can still exert gravity on an airplane in mid-air.įorce is a vector measurement, so there is always a direction associated with it. Any two objects, provided they are interacting with each other, will exert a force on each other. These pushing and pulling interactions between objects are called forces. And when she collides with the Earth (hopefully, lightly!) the Earth is, in effect, pushing on her, causing her forward motion to slow down quite quickly and stop. When she deploys her parachute, the parachute pulls her upward, causing her to go slower. Our parachutist is being pulled toward the Earth by the Earth’s force of gravity, causing her to go faster. In order for an object to change its speed, something needs to act on it: an object either needs to get pushed or pulled in a certain direction. Dynamics is the study of the causes of the different motions: uniform and non-uniform. What happens when you hit the brakes in a car that makes you come to a stop, or what happens to the parachutist as she jumps out of the plane that makes her fall faster and faster - this is the study of dynamics.
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