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Transcript
FORCES AND MOTION HOW DO FORCES AFFECT OBJECTS? • Force- a push of pull that one object exerts on another. • Forces can change the motion of the object. • A baseball batter uses force to hit the ball and that hit changes the direction of the ball. • Forces can also change the shape of objects. • You use force to crush a soda can. 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. 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. HOW DO OBJECTS ATTRACT? • Gravity- a force of attraction that occurs between any object that has mass. • Gravity is a force that only pulls. • The larger the mass of an object, the more gravitational pull it has. • The Earth’s gravity is much larger than a person’s, so we can feel the gravity of the Earth more than we can feel the gravitational pull of others. WHAT AFFECTS GRAVITY? • The force of gravity between two objects depends both on the masses of the two objects and the distance between the objects. • The closer the objects are to each other, the stronger the force of gravity they exert on each other. • Weight- is the force of gravity between the Earth and the object. • Weight is measured on a scale. • Each planet pulls on an object’s mass differently which affects its weight. 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 NEWTON’S FIRST LAW? • Newton’s First Law of Motion- “An object in motion tends to stay in motion, and an object at rest tends to stay at rest.” • An object’s velocity can only be changed by applying a force to it. • Motion can only be changed by applying a force. • Inertia- the tendency of an object to oppose any change in motion. HOW DOES INERTIA AFFECT YOU? • 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. WHAT MAKES OBJECTS TRAVEL IN A CIRCLE? • An object that is traveling in a circle is accelerating even if it moves at a steady speed. • It accelerates because its direction of travel is constantly changing. • The pull of a string keeps the object moving. • Once the string breaks, there will no longer be any unbalanced force on the object. Its inertia will carry it straight ahead at a constant speed.