# Newtons Three Laws of Motion Law 1 Newtons

• Slides: 30

Newton’s Three Laws of Motion – Law #1

Newton’s First Law: This Law has two parts ~ 1) An object at rest will stay at rest unless it is acted upon by an unbalanced force. 2) An object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

• The first law is also known as the Law of Inertia. • Inertia: two definitions: 1) the tendency of an object to keep doing what it’s already doing 2) An object’s resistance to change its speed and/or direction (its velocity)

• Anything with mass has inertia. • . All matter (solids, liquids, and gases) has mass therefore all matter (solids, liquids, and gases) has inertia.

• The more mass an object has, the more inertia it has. • More massive objects are harder to stop and start moving. • Example: Bowling ball vs. Ping Pong ball * A bowling ball has more mass, therefore more inertia, and is harder to move. * A ping pong ball has less mass, therefore less inertia, and is easier to move.

• The more velocity an object has, the more inertia it has. • . Faster moving objects are harder and take longer to stop. • Example: Running vs. Walking * If you are running down the hall and someone steps in front of you, you are more likely to run into them. * If you are walking down the hall and someone steps in front of you, you are less likely to run into them.

Inertia Video: Enter the number 1 in the box below the screen. Inertia begins at 1: 24 ends at 4: 50 http: //www. animatedscience. co. uk/flv/

• According to the First Law of Motion: o Once an object is moving, it will keep moving until an unbalanced force causes it to stop. o If an object is at rest, it will stay at rest until an unbalanced force causes it to move.

o If an object is moving in a northward direction, it will continue moving northward until an unbalanced force causes it to change direction. o Remember, an object’s motion will only change when an unbalanced force acts upon the object.

Balanced vs. Unbalanced Forces Unbalanced: § The forces on the object are NOT equal in size § The net force is NOT zero. § The forces may be in the same or opposite direction(s). § The object DOES experience a CHANGE of motion; changes direction and/or speed.

Remember number lines? positive • Going to the right is __________. • Going to the left is ___________. negative Figure the net force the same way: Give arrows going to the right a positive number and arrows going to the left a negative number.

• Example #1: 20 N 40 N 20 -40 o Figure the net force: _____ + _____= _____ -20 N o The net force is _______ o The net force is _____ zero, therefore it is NOT _________. unbalanced o The box will be moving to the ______with a force left of _____ ___. 20 N

• Example #2: 60 N 10 N 60 0 70 o Figure the net force: ___ + ___= _____ 10 70 N o The net force is _______ o The net force is _____ zero, therefore it is NOT _________. unbalanced o The box will be moving to the ______with a force right of _____ ___. 70 N

Remember graphing quadrants? • Going up is _____. positive negative • Going down is _____. Figure the net force the same way: Give arrows going up a positive number and arrows going down a negative number.

• Example #3: 10 N 20 N -10 20 10 o Figure the net force: _____ + _____= _____ 10 N o The net force is _______ NOT o The net force is _____ zero, therefore it is unbalanced _________. up o The box will be moving ______with a force of 10 N _____ ___.

• Example #4: 30 N 20 N 80 N 20 N o Figure the net force: 20 -50 -20 _____ + ____= _____ -80 30 -50 N o The net force is _______ NOT o The net force is _____ zero, therefore it is _________. unbalanced left o The box will be moving to the ______with a force of _____ ___. 50 N

Balanced: • The forces on the object are equal in size • The net force is zero. • The forces are in opposite directions. • The object experiences no change of motion. • The object is either at rest or moving at a constant speed. • Balanced forces have the same effect as no force. (Remember with no force, the object will keep doing what its already doing. )

• Example #1: 20 N 20 -20 o Figure the net force: _____ + _____= _____ 0 zero N o The net force is _______ o The net force _____ zero, therefore it is IS _________. balanced o The box will either be at _____ or _____ at a rest moving constant _______ speed.

• Example #2: 5 N -5 5 o Figure the net force: _____ + _____= _____ 0 0 N o The net force is _______ o The net force _____ zero, therefore it is IS _________. balanced o The box will either be at _____ or _____ at a rest moving constant _______ speed.

• Example #3: 10 N o Figure the net force: 10 0 -10 _____ + ____= _____ -10 10 0 N o The net force is _______ IS o The net force _____ zero, therefore it is _________. balanced rest moving o The box will either be at _____ or _____ at a constant ______ speed.

• Example #4: 40 N 10 N o Figure the net force: 40 0 -40 _____ + ____= _____ -10 10 10 N 40 N o The net force is _______ IS o The net force _____ zero, therefore it is _________. balanced rest moving o The box will either be at _____ or _____ at a constant ______ speed.

• In outer space, there are no unbalanced forces. There is no air therefore no air resistance (which is a type of friction). There is also no gravity. Therefore, with no unbalanced forces, a space ship launched with a certain speed and direction will keep going at that same speed and in the same direction forever!

• On Earth, however, there always unbalanced forces, such as air resistance and gravity. Therefore an object can’t keep moving forever on Earth.

Examples of the 1 st Law: 1) If you slide a book across the table it will come to a stop due to the force of friction acting upon it. 2) If you throw a baseball upward it will eventually slow down and come back down due to the force of gravity acting upon it.

3) A soccer ball will stay sitting at rest until an unbalanced force like a kick changes its motion. 4) A vacuum chamber on earth will have no air, therefore no air resistance, but will still have gravity. This allows us to see that objects fall to the ground at the same rate without air resistance, like a bowling ball and a feather! https: //www. youtube. com/watch? v=E 43 -Cfuk. Egs (4. 41 length)

5) Wearing a seatbelt in the car protects you from your own inertia. If you are in a car going 65 mph and the car suddenly stops, your body keeps moving at 65 mph until it comes in contact with a force to stop it. | Better a seatbelt than the windshield!

6) When you top a hill and go down the other side quickly, you can get a “floaty” feeling. This is because your body wants to keep moving upward, but it’s being forced downward. 7) When you are forced up a hill quickly you can get a “heavy” feeling. This is because your body wants to keep moving downward, but it is being forced upward.

ADD GRAPHS Slowing Down Speed (m/s) Speeding Up Time (s)

ADD GRAPHS At Rest Speed (m/s) Constant Speed Time (s)