force

defining force

Force is defined as a push or pull acting on an object. There are several fundamental forces in the universe, including the force of gravity, electromagnetic force, and weak and strong nuclear forces. When it comes to the motion of everyday objects, however, the forces of interest include mainly gravity, friction, and applied force. Applied force is force that a person or thing applies to an object. Q: What forces act on Carsons scooter? A: Gravity, friction, and applied forces all act on Carsons scooter. Gravity keeps pulling both Carson and the scooter toward the ground. Friction between the wheels of the scooter and the ground prevent the scooter from sliding but also slow it down. In addition, Carson applies forces to his scooter to control its speed and direction.

force as a vector

Force is a vector, or a measure that has both size and direction. For example, Colton pushes on the ground in the opposite direction that the scooter moves, so thats the direction of the force he is applies. He can give the scooter a strong push or a weak push. Thats the size of the force. Like other vectors, a force can be represented with an arrow. You can see some examples in the Figure 1.2. The length of each arrow represents the strength of the force, and the way the arrow points represents the direction of the force. Q: How could you use arrows to represent the forces that start Coltons scooter moving? A: Colton pushes against the ground behind him (to the right in the Figure 1.1). The ground pushes back with equal force to the left, causing the scooter to move in that direction. Force arrows A and B in example 2 in the Figure 1.1) could represent these forces.

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force and motion

Forces cause all motions. Everytime the motion of an object changes, its because a force has been applied to it. Force can cause a stationary object to start moving or a moving object to change its speed or direction or both. A change in the speed or direction of an object is called acceleration. Look at Carsons brother Colton in the Figure starts the scooter moving in the opposite direction. The harder he pushes against the ground, the faster the scooter will go. How much an object accelerates when a force is applied to it depends not only on the strength of the force but also on the objects mass. For example, a heavier scooter would be harder to accelerate. Colton would have to push with more force to start it moving and move it faster. Q: What units do you think are used to measure force? A: The SI unit for force is the Newton (N). A Newton is the force needed to cause a mass of 1 kilogram to accelerate at 1 m/s2 , so a Newton equals 1 kg m/s2 . The Newton was named for the scientist Sir Isaac Newton, who is famous for his laws of motion and gravity.

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instructional diagrams

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questions

fundamental forces of the universe include

a) gravity.

b) friction.

c) electromagnetic force.

-->  d) two of the above

the main forces that affect the motion of everyday objects include

a) gravity.

b) friction.

c) applied force.

-->  d) all of the above

only some changes in speed or direction are caused by forces.

a. true

-->  b. false

the force required to change an objects motion depends on the objects mass.

-->  a. true

b. false

force is a vector.

-->  a. true

b. false

diagram questions

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