What are Forces?
Pushes and Pulls Force- a push or pull that acts on an object. Forces make a moving object speed up, slow down, or change direction. Forces have both magnitude and direction. Magnitude is measured in newtons (N). Direction is the way the force is acting. Example- an apple falling on a tree exerts a downward force with a magnitude of about 1 newton.
How Do You Measure Forces? To measure force we use a spring scale. Measured in Newtons Friction- a force that opposes the motion of the object sliding over another. If you pull an object with a spring scale along a surface, you can feel the object resist the sliding.
Gravity Every object in the universe exerts a gravitational pull on every other object. Only gravity of a large object such as Earth is strong enough to be felt. Earth s gravity pulls objects toward its center without touching them. An object s weight is the amount of gravitational force between it and Earth. The weight depends on the object s mass and Earth s mass, the size of the Earth, and how far above the Earth the object is.
Magnetism and Electricity Magnetism- a force that pushes and pulls on other objects. The force is greatest at the poles. Magnets strongly pull objects made of iron, cobalt, nickel, and gadolinium. Magnets exert forces on other magnets. Electric Forces- act between objects that are electronically charges. Objects become electrically charges when they gain or lose electrons. All objects that are electronically charged will exert forces on each other. Oppositely charges objects are attracted to each other. Objects with the same charge are repelled, and may move away from each other.
Gravity, Electricity, and Magnetism Like gravity, magnetic and electric forces can act between objects even if the objects do not touch. All 3 forces increase as objects get closer together. The forces of magnetism and electricity between objects can be blocked by putting certain kinds of materials between the objects. Gravity can t be blocked. Electricity and magnetism can push or pull on different objects. Gravity exerts only a pulling force on objects.
Friction Friction- the force that results when two materials rub against each other. Friction acts to slow down the motion of an object or keep it from starting to move. Friction depends on the objects involved. Shape, speed, and texture affect friction. Air and water resist motion when a moving object pushes against them. Air friction is present when air flows over a surface. Flowing water has a similar kind of force.
What are the Types of Friction? Friction acts anytime the surfaces of objects are in contact. 3 kinds of friction: Sliding Friction: When opposite forces push across. Static Friction: Prevents the start of any movement between surfaces in contact. If the surface is smother or steeper, there might not be enough to hold an object in place. Rolling Friction: Friction allows wheels to move us forward. Friction between wheels and the ground push an object ahead.
How Do Drag Forces Act? Drag Motion- when an object moves through a gas, like air, or any liquid, there is a force that opposes motion. The object moves through air, the air molecules bump into it, which causes the object to slow down. Similar to sliding friction because they both oppose motion. Drag force depends on speed, size, and shape. Speed: the faster the speed the greater the drag.
What are Balanced Forces? Net Force- combined effect of the forces acting on an object. When the forces acting on an object are equal the net force is 0 and the object doesn t move. Anytime two or more forces completely offset one another, we say they are balanced forces. When the forces on an object are balanced, the net force on the object is zero.
What Are Unbalanced Forces? Unbalanced forces- When the force or forces acting on an object do not completely offset one another. The leftover force can be represented as a single push of pull in a certain strength and direction. When a net force is unbalanced, it means the net force is not at zero.
What is Inertia? Inertia- the tendency of an object to oppose any change in motion. Jolting forward when a bus stops quickly is only one way you tend to keep moving because of inertia. Inertia is why seatbelts are so important. You might be able to control yourself in a car when you know it is going to make a turn, it is almost impossible to control your movement in a car that suddenly stops or changes direction. Seatbelts keep you moving with the car or stop you from moving when the driver breaks.
Work and Power Work- when a force moves an object. Formula: force distance = work Measured in Joules. If the force applied to an object does not make the object move, then no work has been done. Work is only done when the object moves at least partly in the same direction in which the force is applied. Power- the rate at which work is done. When work is done faster, power is increased. Formula: work time = power