1. FORCES AND MOTION

2. FORCE A force is any push or pull from one object to another.

3. TYPES OF FORCES Magnetic force Gravity Friction force Where have you observed magnetic force? Toys and magnets Where have you observed the force of gravity? Falling objects, planets held in orbit by gravitational pull of the Sun, tides Where have you observed friction force? When sliding an object to move it across the floor, skiing and skating, a car’s tires rubbing against the road

4. WHAT IS USED TO MEASURE FORCE? A Spring Scale

5. AIRPLANE FORCES Engines push or pull a plane forward. This is called thrust. As a plane moves forward, air moves around the wings and creates a force that raises the plane into the air. This force is called lift. A pull called drag slows a plane down.

7. WE USE FORCES IN MANY WAYS. Forces are used to crush, stretch, or twist objects and deform them. What is an example of how we use crush? Crushing an aluminum can. The harder a substance is, the more force it takes to change its shape.

8. FORCE A force can cause an object to start moving, speed up, change direction, slow down, or stop. Each of these involve accelerations. Forces accelerate objects when they affect their motion.

9. HOW IS A BAT HITTING THE BALL A FORCE? The bat contacts the ball, pushing it in the opposite direction through the air.

10. WHAT FORCES ARE EXERTED ON THE AIRPLANE AS IT IS FLYING? Thrust, lift, drag, and weight

11. HOW COULD YOU MAKE AN AIRPLANE RISE FASTER INTO THE AIR? Increase its lifting force by changing the wings to increase lift. Design it to have less wind resistance. Decrease its mass to make it lighter.

12. GIVE AN EXAMPLE OF A FORCE THAT CHANGES BOTH AN OBJECT’S SHAPE AND MOTION. When a piece of clay is thrown against a hard surface, the hard surface will apply a force to the clay. This force will stop the clay (change in motion) and deform it (change of shape).

13. WHAT CAUSES A DROPPED OBJECT TO FALL TO THE GROUND? Gravity

14. IF AN OBJECT WERE DROPPED ON THE MOON’S SURFACE, WOULD IT FALL TOWARD EARTH OR TOWARD THE MOON? Toward the Moon

15. SOME GRAVITY EXISTS BETWEEN YOU AND THE PERSON NEAR YOU. WHY ARE YOU PULLED TOWARD EARTH AND NOT TOWARD THE OTHER PERSON? Gravity depends on mass, and Earth has a much greater mass than a person. Gravitational attraction is not just between an object and Earth. Gravity exists between any two objects.

16. WHAT IS NEWTON’S LAW OF UNIVERSAL GRAVITATION? Sir Isaac Newton believed that every object in the universe was pulling on every other object. This theory is called Newton’s Law of Universal Gravitation. Newton stated that gravity depends on the masses of the objects and the distance between them. Increasing the mass increases the force and increasing the distance decreases the force.

17. FRICTION Friction is the force that opposes the motion of one object moving past another. Friction depends on the surfaces of two objects and how hard the objects are pushed together. Smooth surfaces usually have less friction than rough surfaces. Friction increases when surfaces are pressed together with greater force. Friction also increases with the weight of an object.

18. Rubbing your hands together is an example of friction. The friction causes the hands to slow down as they are rubbed and this generates heat. Heat is created whenever there is friction.

19. HOW COULD YOU INCREASE THE TRACTION (FRICTION) OF CAR TIRES ON AN ICY ROAD? 1.Increase the weight of the car 2.Make the tires rougher with better tire tread or chains

20. WHAT WOULD THE WORLD BE LIKE WITHOUT FRICTION? Without friction, you would not be able to walk or move around because your feet would slip on everything!

21. BALANCED FORCES When forces act on an object without changing its motion they are called balanced forces.

22. UNBALANCED FORCES A force that causes an object to change its motion is called an unbalanced force.

23. NEWTON’S FIRST LAW OF MOTION Newton’s First Law of Motion states that objects do not change their motion unless forced to do so. “An object at rest tends to stay at rest, and an object in constant motion tends to stay in motion, unless acted upon by an unbalanced force.” It is sometimes referred to as the law of inertia. This law describes inertia.

24. HOW COULD YOU KEEP A BALLOON FROM RISING OR FALLING IN AIR? You could use balanced forces. The force of gravity would have to be balanced by another force. This could be done using the force of buoyancy. A balloon could be made to hover in the air without rising or falling if it were filled with hot or light gas.

25. HOW DOES NEWTON’S FIRST LAW EXPLAIN HOW SEAT BELTS PREVENT INJURIES IN CAR ACCIDENTS? During car accidents, a car undergoes sudden decelerations. Your body, however, keeps traveling in a straight line, possibly through the windshield. Seat belts provide an outside force that changes your motion and brings you to a stop.

26. NEWTON’S SECOND LAW OF MOTION Newton’s Second Law of Motion states, “The unbalanced force on an object is equal to the mass of the object multiplied by it acceleration.” F = m x a What do the symbols F, m, and a stand for? F is for force, m is mass, and a is acceleration.

27. WHAT COULD YOU DO TO A RACE CAR TO MAKE IT ACCELERATE FASTER? You could increase the total force that is acting on the race car by reducing friction and drag or by increasing the power of the engine. You could also decrease the mass of the race car.

28. WHAT WILL HAPPEN TO THE ACCELERATION OF AN OBJECT IF YOU DOUBLE BOTH THE MASS AND THE UNBALANCED FORCE ACTING ON IT? The acceleration will stay the same.

29. NEWTON’S THIRD LAW OF MOTION Newton’s Third Law of Motion states, “All forces occur in pairs, and these two forces are equal in strength and opposite in direction.” For every action there is an equal but opposite reaction.

30. ACTION AND REACTION FORCES When one object pushes on a second object, the second pushes back on the first with the same strength. The push of the first object on the second is called the action force. The push of the second object back on the first is called the reaction force.

31. HOW COULD A TOY ROCKET ACCELERATE AFTER TAKEOFF? The toy rocket might fire hot gases downwards out of its engine. The reaction force from the gases would push the engine (and rocket) upwards.

32. WHAT ARE THE ACTION AND REACTION FORCES ACTING ON YOUR BODY WHEN YOU WALK? Feet push down on the road, which in turn pushes up on the feet. The reaction force balances gravity. The feet also push backward on the road and the road pushes forward on the feet. This reaction force propels you forward.

33. SUPPOSE A CAR IS TRAVELING DOWN THE HIGHWAY AND A BUG HITS THE WINDSHIELD. WHAT ARE THE ACTION AND REACTION FORCES? The bug exerts an action force on the windshield, and the windshield exerts an equal but opposite reaction force on the bug.

34. SUPPOSE A LARGE ROCK INSTEAD OF A BUG HIT THE WINDSHIELD. WHAT WOULD THE EFFECT BE? The action and reaction forces would again be equal, but greater than the forces with the bug. If the forces were great enough, the windshield might crack.