1. Physics: Forces and Motion

2. Speed Speed: the distance traveled by an object during a given time
Average Speed = Distance
Time
S = D T

3. Example
A cheetah ran 4 km in 2 minutes. What was the cheetah’s average speed?
S = D * Don’t forget units! * T
S = 4 km
2 min
S = 2 km/min

4. Finding Distance and Time
What if you are given the speed but have to find the distance or the time?
Original formula:
S = D T
D = S X T
T = D S

5. Examples If a coyote can run at 43 mph, how far can one go in 30 min?
Make sure your units match up!
D = S X T
D = 43 mph X hrs
D = mi

6. What would your answer be in minutes?
Examples cont.
If a black mamba can slither at 20 mph, how long would it take to go 1 mile?
Make sure your units match up!
T = D S
T = 1 mi
20 mph
T = 0.05 hr
What would your answer be in minutes?
0.05 hours X 60 min = 3 min

7. Velocity Velocity: Speed that has a Direction
A car that is moving 40 mph West
A person that is walking 3 mph Northeast
A ball that was thrown 2 mph “up”

8. Acceleration Acceleration: the rate at which velocity (speed) changes
Can be changes in speed
Bus moving down street
Can be changes in direction
Staying same speed around a curve on a bike
Can be changes in both speed and direction.
Roller coaster

9. Calculation Accleration
Acceleration= change in velocity
total time OR
a= (vfinal-vintial) t

10. Force Force: a push or pull that acts on an object
Causes resting objects to move
Causes moving objects to accelerate
Measurement: Newton (N)
Representation: Arrow

11. Balancing Forces Balanced Force: no movement
Unbalanced Force: object(s) forced to accelerate

12. Friction Friction: force slows down an object as the object moves past
Without friction: walking on ice
Static Friction: force acting on
object at rest
Sliding Friction: opposes direction of object in motion

13. Gravity
Gravity: Force that acts downward toward the center of the Earth
Does not require contact to act
Upward force usually balances the force of gravity
Falling Objects: Gravity causes objects to accelerate downward
Air resistance is the balancing force

15. Terminal Velocity
Terminal Velocity: velocity of object when air resistance equals force of gravity

16. Newton’s Laws of Motion
Isaac Newton: Important in the study of mass, force and motion
Newton’s 1st Law of Motion: the motion of an object does not change as long as the net force is zero
Object won’t move unless something moves it!!
Object won’t stop moving unless something stops it

17. Newton’s Laws of Motion
Newton’s 1st Law of Motion
a.k.a Law of Inertia:
Soccer ball won’t move until someone kicks it
Soccer ball will keep moving after kicked until something stops it

18. Newton’s Laws of Motion
Newton’s 2nd Law of Motion
Force of an object is equal to the mass times the acceleration of an object
F =ma
What is the force of an object with an acceleration of 12 m/hr2 and a mass 1000 kg?

19. Newton’s Laws of Motion
Newton’s 2nd Law of Motion
Also applies with a force that acts in the opposite direction
In a collision, the seatbelt applies a force that opposes a person’s forward motion

20. Newton’s Laws of Motion
Newton’s 3rd Law of Motion: Whenever an object exerts a force on a second object, the second object exerts an equal and opposite force on the first object
For every action there is an equal and opposite reaction
Called ACTION AND REACTION forces

21. Newton’s Laws of Motion
Action Reaction Forces
Hand pushing on wall: action force
Wall pushing on hand: reaction force
Doesn’t mean an object won’t move
If the action reaction forces are on the same object…no movement
If the action reaction forces are on different objects….movement can occur

22. Momentum
Momentum: Inertia in motion. Momentum is determined by multiplying the mass and velocity of an object.
The larger the mass, the more momentum
The larger the velocity, the more momentum
Momentum= Mass x Velocity
p=mv

23. Momentum
Two cars collide. Car A has a mass of 5000 kg and was traveling 35 km/hr west.
Car B has a mass of 1000 kg and was traveling 35 km/hr east.
After the collision, what direction did both cars travel

24. Collisions - Elastic
Elastic – a collision in which the total kinetic energy of the objects before and after collision is equal
Two objects collide and bounce off one another.

25. Elastic Collisions

26. Collisions - Inelastic
Inelastic - a collision in which kinetic energy is not conserved. (the kinetic energy before and after the collision is NOT equal)
Two objects collide and stick together and move with the same velocity

27. Inelastic Collisions

28. What kind of collision is this?

29. What kind of collision is this?

30. What kind of collision is this?

31. What kind of collision is this?

32. What kind of collision is this?

33. Sources